CTV & OTT glossary: 24 terms in plain language
Every term you will meet while monetizing Connected TV inventory or buying CTV campaigns — defined in two or three honest sentences, with a link to the guide that goes deeper.
CTV (Connected TV)
Any television set connected to the internet and used to stream video — directly through a smart TV platform or through an external device such as a streaming stick, set-top box or game console. In advertising, CTV refers to video ads shown on that big screen inside streamed content.
OTT (Over-the-Top)
Video content delivered over the internet directly to viewers, bypassing cable, satellite or broadcast operators. OTT describes the delivery method; CTV describes the device. An OTT ad watched on a television screen is, in practice, CTV advertising.
FAST (Free Ad-Supported Streaming TV)
Linear, scheduled streaming channels that viewers watch free of charge, monetized entirely through ad breaks — the streaming-era equivalent of traditional broadcast TV. FAST channels are usually operated as apps or channels on CTV platforms and rely on server-side ad insertion.
AVOD (Advertising-Based Video on Demand)
On-demand video that is free for the viewer and funded by advertising — pre-roll and mid-roll ads inside a content library. Unlike FAST, the viewer chooses what to watch and when; unlike SVOD, no subscription is charged.
SVOD (Subscription Video on Demand)
On-demand video paid for by subscription rather than advertising. Some subscription services run hybrid tiers where a cheaper plan includes ads, in which case that tier behaves like AVOD for monetization purposes.
In-stream video (pre-roll / mid-roll / post-roll)
Video ads that play inside video content: before it (pre-roll), at a break inside it (mid-roll) or after it (post-roll). On CTV these are typically 15 or 30 seconds long and non-skippable, which is why completion rates are far higher than on mobile.
Ad pod
The sequence of ads inside one ad break — the streaming equivalent of a TV commercial block. Pod length, the number of ads, competitive separation between rival brands and repetition rules are configured in the ad server or SSAI system.
VAST (Video Ad Serving Template)
The industry-standard XML format in which an ad server answers the question 'which ad should I play'. A VAST response contains the video file URL, tracking events (impression, start, quartiles, complete), click-through destination and error callbacks. Players request a VAST tag at each ad break.
VPAID (Video Player Ad Interface Definition)
A legacy standard that allowed ads to execute their own code for interactivity and measurement. Powerful but heavy, it is effectively deprecated on TV platforms for performance and security reasons; OMID has replaced it for measurement.
OMID (Open Measurement Interface Definition)
The IAB standard interface that lets independent verification vendors measure viewability and completion inside a video player without custom code per vendor. Supporting OMID widens demand, because brand buyers are contractually limited to measurable inventory.
SSAI (Server-Side Ad Insertion)
Ad insertion done in the cloud: ads are stitched into the video stream on the server before it reaches the device, so playback is smooth, consistent across platforms and resistant to ad blocking. The standard approach for FAST channels and live streams; measurement must be designed deliberately because the player no longer knows where ads are.
CSAI (Client-Side Ad Insertion)
Ad insertion done by the video player on the device: it pauses content, calls the ad server, plays the ad and returns to content. Precise and fully measurable from the client, but requires the player to handle VAST parsing, timeouts and transitions on every supported device generation.
SCTE-35
The standard marker format embedded in a video stream that signals where ad breaks begin and end. SSAI systems rely on these cue points to place ads; wrong or missing markers are the most common technical cause of broken FAST monetization.
ads.txt (Authorized Digital Sellers)
A plain-text file on a web domain listing who is authorized to sell that inventory. Buying systems crawl it automatically and drop unauthorized supply, which makes it one of the highest-leverage trust signals a publisher can publish.
app-ads.txt
The extension of ads.txt to mobile and CTV apps: the same authorization file, referenced from the app store listing. Because CTV inventory lives in apps rather than websites, app-ads.txt is effectively mandatory for serious CTV monetization.
sellers.json
A file published by ad systems that discloses who the sellers in a transaction are. Together with the SupplyChain object in the bid request, it lets buyers trace every hop between their money and the publisher's screen.
SupplyChain object (schain)
A standard object in programmatic bid requests listing every intermediary that touched the impression. Buyers use it with ads.txt and sellers.json to verify they are buying from a legitimate, declared path — opaque chains are increasingly filtered out.
Fill rate
The share of ad opportunities that actually return an ad. Unfilled breaks are lost revenue that never appears in a CPM report, so fill should be monitored per placement and per GEO rather than as a single average.
CPM (Cost per Mille)
The price a buyer pays per thousand ad impressions — the primary pricing unit for CTV inventory, where completed views are the norm. Real CPM levels depend on audience geography, content genre, season and verification status.
eCPM (effective CPM)
A publisher's effective revenue per thousand impressions across all demand, fill included: revenue divided by impressions, times a thousand. A high-CPM source with poor fill can earn less than a moderate one that fills everything — eCPM is the honest comparison metric.
Frequency capping
A limit on how many times the same household or device sees the same ad within a period. On CTV, frequency caps are enforced by the ad server or SSAI and protect both viewer experience and advertiser budgets from over-exposure.
Device spoofing
Fraud in which cheap traffic — phones, emulators or servers — pretends to be a smart TV in order to sell at CTV prices. Verification vendors detect it through device-graph and behavioral analysis; publishers defend themselves by keeping inventory verifiable.
Co-viewing
Several people in a household watching the same screen at once. One CTV impression can therefore reach multiple viewers — a structural advantage of the big screen that measurement models account for with co-viewing factors.
Addressable TV / household targeting
Serving different ads to different households watching the same content, based on household-level signals such as geography, demographics and interests. This is what separates CTV from traditional broadcast: targeting is broader than device-level mobile targeting but far richer than linear TV.