The Endicor system was a star system.

In the mid-24th century, this system was far away from other Federation ships or starbases.

In 2365, this was the destination of the USS Enterprise-D after visiting Starbase 73. En route, it encountered an energy vortex which threatened the ship. It escaped through an encounter with a future duplicate of its own Jean-Luc Picard six hours in the future. (TNG: "Time Squared")

This star system was only mentioned in dialogue.
A planet named Endicor (β) had previously been mentioned in issues 49-50 of the Star Trek comic book, published approximately a year before "Time Squared" was produced. Whether the Endicor system in "Time Squared" was named in reference to the planet in the comic is unknown.