"Limp" means "soft" and "weak". Imagine a French fry that's been left out for a few hours. It's not crispy any longer; it hangs down when you hold it and feels soft. That's the meaning of "limp".
A "limp" handshake is when someone shakes hands without enough pressure. The correct handshake is a firm handshake. This means to grab the other person's hand and squeeze it just a little bit. But some people just hold the other person's hand without squeezing. This is called a "limp" handshake, and most people don't like it.
Other examples of "limp" things include:
- Someone's body when they're dead, asleep, or passed out.
- Hair that's thin or oily.
The word "limp" is also used in some embarassing sexual situations. Use your imagination to figure out what that might be.