A format defines the conditions, such as the file size and dimensions, that a creative must meet in order to avoid errors while uploading the creative file. A format does not necessarily need to be an online banner ad, it could be a native or video ad as well. All imaginable formats are possible, as long as they fit into the inventory’s structure or website design and connect with your strategy.
Refer to the Appendix Online advertising formats for a definition of the most important formats and a representation within their environment. The overview is not exhaustive. A publisher can implement custom formats as well.