Block a person so they can no longer see your profile, message you, or find you on Facebook.
Search their name in the Facebook search bar and tap their profile. This works the same in the app on iPhone and Android and on the website.
On their profile, tap the three-dot button near their name (next to the Message or Add Friend buttons). A menu of profile actions opens.
Tap Block, review what blocking does, and confirm. Facebook unfriends you both automatically; they are not notified, but they may notice your profile has disappeared.
If their profile is hidden from you, open Settings & privacy, then Settings, and search for Blocking. Add their name or profile link to the Block list directly from there.
You can unblock anyone from the same Blocking settings page, but you must wait 48 hours before you can block them again, and unblocking does not restore the friendship.