Ad Slot

An ad slot is a single playout window on a DOOH screen — typically 10 to 30 seconds — during which exactly one creative plays. A screen running a 30-second slot every 90 seconds delivers 40 ad slots per hour, which (multiplied by the sensor-counted audience per slot) becomes the per-hour impression count.

On the buy side, an ad slot is the atomic unit a DSP bids on. The bid request describes the slot's properties — venue category, screen dimensions, expected audience size, time of day — and the DSP returns a creative URL and a bid for that one slot. There is no concept of a "campaign slot" in OpenRTB 2.6: every slot is auctioned independently.

Slot length matters for two reasons. First, a longer slot has more time to fire quartile events through VAST, which means cleaner viewability measurement. Second, the per-slot CPM is roughly proportional to slot length up to about 20 seconds, after which buyers discount for diminishing attention. The Trillboards default is 15 seconds — long enough for clean quartile measurement, short enough to maintain CPM efficiency.

Compare to a "loop" — the full sequence of slots a screen plays before repeating. A 10-slot loop with 30-second slots is a 5-minute cycle. Loop frequency is what controls frequency capping in DOOH.