Why is there a "mean" in "Greenwich Mean Time" (GMT)?

Question

What's the meaning of the word "mean" in "Greenwich Mean Time"?Shouldn't we simply say something like "Greenwich Time"? I don't understand what the word "mean" is doing there.

Answer 1

The Greenwich mean time is called Greenwich mean time because the PRIME meridian passes through Greenwich, a village near London.

Answer 2

Mearn or meridian are other ways of describing lines of longitude. By internation agreement, the line of longitude, or mean, than passes through Greenwich England is zero and all other time zones are plus or minus from Greenwich mean time.