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.