Gaining an understanding of Row and Filter Context is among the most difficult challenges facing a new DAX author. Just when you think you've got it, a problem arises and your hard-won mental model seems to crumble before your eye. For a new author this is particularly tricky in that virtually everything beyond the most trivial measures relies heavily on these concepts; forcing most new folks to resort to memorizing patterns until that mental model develops naturally.
In this video, we're going to attempt to jumpstart that process. This isn't a strict technical definition (I simplify a few things), but rather a beginner friendly mental model designed to get you up and running with DAX while still giving you a solid sense of what's happening under the hood.
BTW, I squeeze a lot of data on this page; so, unlike most of my videos you're going to want to watch this one in full 1080 (look for the gear at the bottom right of the YouTube player), preferably on a decent sized monitor.