Online marketing has become a messy mix of direct marketing, seo, tricks, tips, code and guesswork. It’s an always-moving target and it’s mostly focused on tactics, not strategy, because tactics are easy to measure.
Marketing online, on the other hand, is what happens when the work to serve our audience arrives in an electronic form. Marketing online is simply marketing–the act of making things better by making things–aided by a mouse and a keyboard.
Careful not to get stuck focusing on the wrong one. You need both, but one drives the other.