First there was a log, a cylindrical portion of wood from a tree. Then someone tied a knotted rope to one and used it to calculate the distance and speed of ship. (These were later refined and standardised.) Then someone recorded distances and speeds, along with other relevant data, in a book. Then someone recorded any recurring data. Then someone recorded it on the world wide web (a world wide web log > blog). Then someone added video (a video world wide web blog > vlog (which I think is a horrible word, not least because vl- is not an allowable initial consonant cluster in English)). Then someone made one about their travels on a motorcycle (a motor bicycle video world wide web log > motovlog) and Youtube suggested that I watch it. The activity and word is common enough that Wikipedia has a short article about it.
Along the way, log, blog and vlog (and probably motovlog as well) also became verbs. Pages for Mac doesn’t like vlog, autocorrecting it to blog and red-underlining it when I change it back, or motovlog, which it doesn’t autocorrect to anything.
There is some variation between motor– and moto– in these kinds of words, but motorhome, motocross and motovlog seem to be more common than their alternatives.
(Surprisingly related to logarithms and their tables and books, being log + arithmós number (compare arithmetic).)