I don't know about others, what I've always understood the definition of "open world" to be is that there won't be any "railroading" of players' agency, hard or soft. That players are free to do their own thing, and not be forced to follow a particular plot, or have regions artificially gated behind certain prerequisites. This is different from a world simply being seamless. A game with a seamless world, that nether-the-less forces you to follow the developer's plot for the game, isn't really an "open world" in my book.what means they give to Open World
For example, Fallout 4 isn't what I would call an entirely open-world game. You're forced to have a spouse of the opposite gender, and a kid, and there are points in the game that you have to follow the game's incredibly obvious plot... eventually. As much as I like the game, that bit of railroading I find a wee bit annoying.