What does VOD primarily refer to in digital advertising?

Video on Demand (VOD) primarily refers to a service that allows users to watch video content whenever they choose, rather than following a traditional schedule. In the context of digital advertising, VOD is significant because it provides an avenue for advertisers to reach consumers through targeted video content distributed on-demand via the internet or through cable services. This method has become increasingly popular as consumers prefer the flexibility of viewing content at their convenience.

While data tracking, ad management, and optimization strategies are important in the broader scope of digital advertising, they do not align with the recognized definition of VOD. Instead, these elements pertain to other aspects of digital media strategies. The focus on delivering video content on demand is a key aspect that makes option A the correct choice, as it encapsulates the primary essence of VOD in the digital advertising landscape.