"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.