Holes is the plural form of hole, which generally refers to an empty space in something solid.
In everyday usage, holes can mean:
1. Physical openings or gaps (e.g. "There are holes in my socks")
2. Difficult situations (e.g. "I'm in a financial hole")
3. Golf term for the cup on the green
4. Slang for problems or flaws (e.g. "His argument is full of holes")
5. In physics, the absence of an electron in a semiconductor