Digital drawings are usually drawn and/or colored on apps such as Photoshop or IBISPaint. They are marketed as editing or paint services. Digital drawing takes a lot of skill and usually one must have some skill in drawing traditionally before attempting a digital. Also, digital drawing can be simple, like in note apps, but lots of professional apps have lots of features and it can take a long time to learn and harness their full potential.
A digital drawing is any drawing colored on an app. Some people make the lineart traditionally and then scan it to be colored in the app.