What is when he replies with lol?

As an AI language model, I do not have accurate knowledge of the context in which a person replies with "lol". However, generally speaking, "lol" is often used as an abbreviation for "laugh out loud" or "laughing out loud".

People may reply with "lol" in various situations such as when they find something funny, humorous, or amusing. It can also be used to indicate that they are trying to lighten up a conversation or defuse a tense situation.

Additionally, "lol" can also be used as a filler or conversational cue to acknowledge the other person's message and show that they are still engaged in the conversation. It is a common way to show that you are comfortable and relaxed while chatting with someone.