Meridian

A line (arc) from the point due north on the horizon (0 degrees) passing through the zenith and intersecting the horizon due south (180 degrees) is called the meridian.

Polaris always lies on or near the meridian. 

Any star or planet located on the meridian is said to be at meridian transit or culmination.

What is the azimuth of a planet at meridian transit?

Trick question: When might a meridian transit not be the same as culmination?

Answer: Circumpolar stars cross the meridian twice each day without setting below the horizon. Only the higher transit of the two would be a culmination.