What is when a guy says a girl is like his sister?

When a guy says that a girl is like his sister, it usually means that he has a close and platonic relationship with her, similar to the bond he shares with his sibling. It is a way of indicating that there is no romantic interest or any kind of attraction towards her. This also implies that he respects and values her as family, and would do anything to protect and support her, just like he would for his sister. It is a sign of a strong and healthy friendship that is built on trust and mutual understanding.