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

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.

According to Wikipedia, Greenwich Mean Time refers to the mean solar time measured at the Royal Observatory in Greenwich.

This article has more information about mean solar time, but it is essentially the mean (in the sense of average) angle of the sun in the sky at any particular time of day. At least insofar as I understand it.

So the mean in Greenwich Mean Time is "average."

As a note, mean solar time is contrasted with apparent solar time, which is based on how long it actually takes for the Sun to return to the same position in the sky. Apparent solar time varies because the Earth's orbit is not perfectly circular, and the Earth speed of the Earth varies according to its distance from the Sun. I think mean solar time is the average of apparent solar time over a solar year.

As has been stated mean in the context of GMT is a type of average.

There are three main types of average: mean, median and mode.

The mean average is where you add up all the number in a list of numbers and then divide the total buy the number of numbers. E.g. the mean of 4,5,6,7,8,9,10 is (4 + 5 + 6 + 7 + 8 + 9 + 10) / 7.

According to Etymonline the meaning is

that which is halfway between extremes

and is from the same word as median.

The median average is where you sort the numbers in a list in ascending numerical order and pick the one in the middle. So the median of 4,5,6,7,8,9,10 is 7.

The mode average is where you pick the number that occurs most frequently in a list. E.g. in 1,1,2,3,4,5,5,5,5,6,7 the mode is 5.

The meaning of mode is related to the French word for fashion, and can be approximately understood to mean most popular.

For more information see this website: http://www.bbc.co.uk/schools/ks2bitesize/maths/data/mode_median_mean/play.shtml