So the word essay originally meant a test (or the act of testing); it comes from the same middle French root as assay. From this sense of weighing or evaluating something, it drifted to mean an attempt, test, or rehearsal; in Portuguese for example the cognate ensaio means exactly that, rehearsal. The modern sense of 'essay' carries this semantic forward in that an essay is, essentially, a take. It's an attempt at saying something about something in a self-contained way, temporally limited both in that it's the perspective of one moment and in that it's meant to be short. A written essay is your 2000-word stab at something.
Which is why it's very funny to me that 'video essay' has drifted to mean specifically the genre of youtube video defined mostly by expanding runtimes. Like almost nothing really stylistically or structurally connects video essayists; a video essay can be narration over archival footage, it can be motion graphics, it can be a talking head, it can be commentary over a reproduced edit of a movie, it can be skits, it can be interviews. But the thing that 'video essay' seems to imply now is that it's at least an hour long, and the longer it is the more it enters the video essay category.
