The definition I'd always heard was "Defending someone with the ulterior motive of making them like you, usually for romantic affection."
But nowadays, I often see the term thrown around for just speaking up for other people generally. It might not even be toward a specific person. Example:
Person A: Man, [x-group] is a bunch of [insult]. Person B: I disagree. There's plenty of good people in that group, and I don't think we should the good in with the bad. Person A: Ugh, you're being such a white knight.
In the above scenario, Person B certainly isn't trying to romantically woo an entire demographic of people, so the original definition of white-knighting obviously wouldn't apply here.
So, has the general meaning changed? Or is the original definition still the more common one that people think of when they hear the term? I don't know if it's just devolved into meaning "defending other people on the internet in any capacity whatsoever" or not, but I am interested in hearing peoples' thoughts on the matter.