To remove someone from your friends list on a social networking site, so that you are no longer connected there. It is a verb: you unfriend someone. Facebook is where the word grew up, and it is still the platform people mean by default; on other apps the word is usually 'unfollow' or 'block', which are different things. The differences matter socially. Unfriending cuts the connection completely and is often a real statement — you are done with this person, or at least done seeing them. Unfollowing quietly hides their posts while you stay connected, so it is the polite, invisible option. Blocking is the strongest: they cannot even find you. So when someone says 'she unfriended me', there is usually a story behind it, and often hurt feelings. The word is worth noticing as a piece of living English. It got common around 2008-2010 and was a word-of-the-year pick, and its shape is unusual: English normally puts un- on adjectives and on verbs meaning 'undo an action' (untie, unlock), but here it was stuck onto a noun, 'friend', to make a brand-new verb. There was also an old, unrelated noun 'unfriend' meaning an enemy, but nobody uses that today.

把某人從（臉書等）好友名單移除、解除好友關係。注意跟 unfollow（只是不看他的貼文，還是好友）和 block（封鎖）不一樣。