And it's not a technical term, but a MARKETING term. An obnoxious and misleading one.
So, I know for example the sentence after you said it contradicts it: "generic and usable in many different ways and usage scenarios". I know DHH first used it, and he named his product "on Rails" precisely because he wanted to make non-developers and beginners feel empowered that they're in the driving seat, while actually not driving at all and running on rails.
Opinionated software is training wheels (or rails). It can't be flexible or general purpose. It constrains you, so that when you don't know what you're doing, you still end up doing something. Children love this, and non-professionals also love it. Experienced professional developers hate it.
It's not fun for professional developers to be told what to do, because they're in the business of they telling computers what to do. And they know libraries can be easy to use and flexible without being "opinionated".
DSLs have their place. But they're not general purpose, it's a contradiction.
And I don't like the term "opinionated" because aside from the smug arrogance with which it's often said around the RoR community, it lies about what it is. It's not "opinionated" - every software is created with opinion, it's impossible for it not to have one. But what the term really means is "constrained". This would suck for marketing though, and DHH is great at marketing, so he came up with that BS instead.
PS: let me also remind you what this word means as an English word: "characterized by conceited assertiveness and dogmatism."