"Reckless driving" is a phrase that means driving very unsafely. A reckless driver might do things like:
- drive way too fast
- drive while typing a text message
- drive through a stoplight that's turned red already
You can get a ticket for "reckless driving" if the police catch you doing something dangerous.
You can also say that a person is "reckless" if they do lots of dangerous things, whether in a car or somewhere else:
He was always reckless: drinking, getting into fights, gambling. It's sad what happened to him, but we all saw it coming.