Think of a unit as a "container." In the case of video advertising, the Unit contains a video player that publishes advertising and content videos with a specific visual format. Technically a Unit is represented by code.
In Viralize you will find two types of Units:
Ad Unit: Units that deliver video or banner advertisements
Content Unit: Units that deliver content videos combined with video ads
There are many parameters you can use to configure a Unit. With experience, you will learn to take advantage of all the Unit formatting possibilities.