Campaign pacing represents a model which is used by campaign delivery engines to make sure that the campaign goal is reached by the time the campaign is scheduled to end, by serving the right amount of impressions to the right audience.
There are two common pacing rules: evenly distributed and front loaded. While front loading makes sure that the campaign objective is fulfilled as soon as possible, the evenly distributed model aims at serving a roughly equal amount of impressions every day until the campaign is scheduled to end.
AudioGO uses an even pacing and the delivery systems strive to distribute the number of impressions served equally throughout the days a given campaign is scheduled to run for. You can read more about how budgets are distributed in AudioGO here.