v.1. Slang To engage in frivolous activity; goof off: The children are fooling around in the yard.
2. Slang fool around with To manipulate or work with something without a clear purpose; toy with something: Who's been fooling around with my briefcase?
3. Vulgar Slang To engage in casual, often promiscuous sexual activity.
4. Vulgar Slang To be sexually unfaithful.