A reply lands at 18:20 from an address you have never emailed: “Quick one, is VTR the same as completion rate?” The client’s brand manager forwarded your September report to someone in the insights team, who forwarded it to a media planner, and the question arrives with no context and a polite apology for asking. You wrote that definition in March. It was three paragraphs into a kickoff email sent to a marketing manager who has since moved to another account. A client report glossary is the obvious fix, and most agencies already have one somewhere. The problem is almost never the writing.
Defining CTR is not difficult work for anyone who buys media for a living. What breaks is everything around the definition: where it sits, who can reach it, and whether it still matches the metrics on the report six months later. A glossary in an onboarding PDF gets one read, on day one, by one person. A glossary pasted into a status email gets buried under fourteen replies about creative deadlines. Both die quietly, and you find out when the definitional questions start again.
So treat the glossary as a placement and maintenance job. Six steps, and the first one is mostly deleting.
An onboarding PDF is where definitions go to die
Go and look at the glossary you already have. It is probably a page in a welcome deck, or an appendix slide at the back of a quarterly review, or a shared doc whose link is in one email thread from last spring. Note two things: how many clicks it takes a stranger to reach it from the report they were forwarded, and whether it mentions a metric you stopped reporting in February.
If the answer to the first is “more than zero,” the glossary is not doing the job. Forwarding is how client reports actually travel. Someone in procurement, a new brand manager, a regional marketing lead, an agency-of-record strategist on the other side of the account, all of them meet your report without meeting you. They will not open an attachment from an email chain they were never on. They will reply to whoever sent them the report, which means the question lands on the client’s desk, and the client forwards it to you.
Keep the old glossary as raw material. Do not keep it as the delivery mechanism.
Your sent folder is the better source list
The instinct is to open a metrics textbook and define everything properly. That produces forty entries, thirty of which nobody asked about, and a document too long for anyone to scan.
Search your sent items instead. Look for the phrases that precede a definitional question: “just to check,” “what does,” “is this the same as,” “sorry if this is obvious.” Pull the last six months across your three or four biggest accounts. What comes back is a much shorter and much stranger list than a textbook would give you, and it tends to cluster around four types of confusion.
Terms that sound like plain English but are not. Reach, frequency, engagement, views. A client reads “views” and thinks somebody watched the ad. On YouTube it means something specific about watch time, and on Meta it means something else again.
Terms that mean different things per platform. VTR is the classic one. A 100% completion rate in DV360, ThruPlay on Meta, a six-second view on a skippable format: these are not the same event, and if your report shows a blended video number across channels, someone will eventually ask what it blends. That question deserves a real answer rather than a definition of “view-through rate” copied from a help centre.
Metrics that look like performance but are cost inputs. CPM moves because of inventory and auction pressure, and a client who reads a rising CPM as a failing campaign will act on it. Related: our piece on the campaign metrics worth putting on a client report is a reasonable check on whether the metric belongs there at all.
Pairs that get confused with each other. Impressions and reach. Clicks and sessions. Conversions and leads. CPA and cost per lead. Define these next to each other, never in separate alphabetical positions where the contrast is invisible.
Ten to fifteen entries covers most accounts. If you get past twenty, some of those terms probably should not be on the report.
Write for the person three forwards down
The reader you are writing for did not commission the campaign, does not know the media plan, and may not work in marketing. Write at that level and the specialists will still be fine. Write for the specialist and the others give up.
A definition that survives has four parts: what the number counts, the unit, what makes it move, and the one sensible way to use it. Skip the etymology and skip the formula unless the formula is the clearest way to say it.
| Instead of | Write |
|---|---|
| CTR: clicks divided by impressions, expressed as a percentage. | CTR: out of every 100 times the ad was shown, how many times someone clicked. Useful for comparing creatives against each other on the same placement. Not a measure of whether the campaign sold anything. |
| CPM: cost per mille. | CPM: what we paid for a thousand ad impressions. It moves with how competitive the inventory is, not with how well the ad performed, so a rising CPM on premium BVOD inventory is usually a market signal rather than a campaign problem. |
| Frequency: average impressions per unique user. | Frequency: on average, how many times one person saw the ad during the period. Low frequency with high reach means we spread wide; high frequency with flat reach means we are hitting the same people repeatedly. |
Two habits to avoid. Do not define jargon with jargon: “VTR measures view-through rate on video inventory” tells nobody anything. And do not put benchmarks in the glossary. “Good CTR is 0.5%” is wrong often enough to be dangerous, and it will be quoted back at you in a renewal conversation. If you want a comparison point, use the account’s own history and put it in the commentary, where it belongs.
Keep definitions out of the monthly commentary
The glossary answers “what is this number.” Your commentary answers “why did it do that this month.” Mixing them makes both worse. The month-to-month text gets padded with explanations the returning reader already knows, and the definitions get stale because nobody thinks of them as a maintained asset.
Practically: the glossary is a fixed block that changes maybe twice a year. The commentary is rewritten every cycle. If you find yourself explaining what VTR means inside a paragraph about why VTR dropped, cut the explanation and trust the glossary panel to be there. That separation is also what lets a report answer questions on its own, which is the whole argument behind why clients reply to reports anyway.
Pin the client report glossary inside the report
Here is the part that decides whether any of the previous work matters. The definitions have to travel with the numbers, in the same object, so that a forward cannot strip them.
If you report by link, put the glossary in the report layout itself: a text block at the bottom, or a collapsed section under the video and audience tables where the vocabulary gets dense. A glossary in the client dashboard costs you a bit of vertical space and saves a recurring email. If you are still sending PDFs, at minimum it goes on a page inside the same file, not as a second attachment, because second attachments get lost in forwarding.
Build it into the template rather than per report. In Screebl a text block in a reusable report template means every report generated from that layout carries the same definitions, in the same place, for every client and every month, without anyone remembering to paste it. Since the report is a shared link behind an access key, whoever the client forwards it to lands on the definitions and the numbers together. And if you have written a campaign brief for the optional report assistant, the more specific “is this VTR blended across channels” questions get answered on the spot, from that one report.
Retire terms as soon as they leave the report
Glossaries rot in one direction: they grow. You add PDOOH definitions for a summer burst, the burst ends, and the entries stay for two years, quietly suggesting to a new reader that the campaign includes channels it does not.
Tie the pruning to a moment you already have. When you change the metric set on a template, or when a campaign type drops off the plan, open the glossary block in the same sitting and delete what no longer appears anywhere on the report. Check it against the KPI tiles and table headers, literally, term by term. Anything defined but not shown comes out. Anything shown but not defined goes in, which is the check that catches the metric a colleague added in month four without telling anyone.
Twice a year is enough for most accounts, plus whenever the media mix changes materially. Ten minutes of deleting, and the glossary stays the length someone will actually read.
The test for whether this worked is not whether the document looks good. It is whether a stranger who receives your report in month seven can answer their own question without emailing anybody. If your reports are still going out as attachments with the vocabulary living somewhere else, have a look at the plans and at what changes when the definitions live inside the report itself.
