What does it mean to go into a wormhole?

Could you please explain in simple terms what exactly is meant by the phrase "going into a wormhole"? I've heard it mentioned in science fiction stories and I'm curious about its theoretical basis in physics. Is it a real phenomenon or just a figment of imagination? If it's theoretical, how does it work and what kind of effects could it potentially have on an object or entity passing through it? Could you elaborate on its characteristics and possible consequences in layman's terms? I'm fascinated by the concept and would appreciate a clear and concise explanation.