1) to admit that you are defeated or cannot do something.
2) to be persuaded to do something you don’t want to do.
(This phrasal verb has more than one meaning)
E.g.1: She wanted a new dress and asked her father to buy it for her. Every time she asked him he said no, but she continued to ask him every day. Eventually he gave in and bought her the dress.
E.g.2: The government refused to give in to the terrorists’ threats.
This phrasal verb cannot be separated.