In its broadest term, digital content refers to data (video, written, information) that can be viewed.
On a digital platform. Within the spectrum of filmmaking, digital content refers to the variety of film or video content generated for specific online use. Content is what is said, form is how it's said. So, content would be things like characters, dialogue, themes, symbols, etc. Form would be how those things are presented - camera movement, pacing, editing, plot structure, etc.