(colloquial) Running or performing extremely smoothly, especially (music, slang) playing perfectly, perfectly in sync with others, or with perfect focus.
Used other than figuratively or idiomatically: see in, groove.
Source: en.wiktionary.orgPeople who care about records are always giving me a hard time. I mean, I would destroy records in performances, and break them, and whatever I could do to them to create a sound that was something else than just the sound that was in the groove. Christian Marclay
A stylus linked to a diaphragm would be made to ride in the groove or on the ridge so that the stylus would be moved back and forth in accordance with the recorded vibrations. Source: Internet
Anecdotes indicate this low-cost arm was the only one capable of keeping the needle firmly in the groove during heavy storms at sea. Source: Internet
I was now 17, wise beyond my years, hip to the haps and smooth in the groove. Source: Internet
The reason records can sound better literally comes down to engineers not being able to squash the music because they need to keep the needle in the groove. Source: Internet
The US is stuck in the groove of saying Pakistan must ‘do more' to eliminate terrorist havens from its soil. Source: Internet