The problem with Google Maps is that they only let you download rectangular chunks of the map one by one (that aren't large enough to e.g. just download a whole state), and then those chunks must be kept regularly updated or they eventually "expire" without you having any say in the matter.

Google Maps also doesn't support offline contour lines / hillshading (what Google calls "terrain"), which is a big deal for hiking and other outdoor activities. Whereas with OsmAnd, you can literally have e.g. the entire North America in your pocket, with contour lines, offline navigation, and offline Wikipedia articles for every POI.

Google times out the downloaded maps without warning, so you go to use them and find out it won't let you use them.

Pointing out more options for people to evaluate is great and all. But at least for me, "offline maps" implies not needing the permission of a surveillance company to use it, and without phoning home to that company when the app regains connectivity. And I'd say that's an appropriate definition in the context of the top level comment about privacy.

It will eventually cease to exist.

I went to Grenada in 2014 and used offline maps to drive around the island. In 2015 the tablet suffered an accident and I powered it off to deal with it later. 5 years later I power it back on without internet connectivity. Turns out the maps expired. So much for many years