Current

http://en.wikipedia.org/wiki/Electric_current

Electric current is the flow of electrons.
Like any measurement it is ultimately completely arbitary but has been standardized to allow people to understand eachother.
Why is linear measurement in inches or mm?
The answer is exactly the same...

"Because it is"
Del

Well this one is a bit different from inches and mm - this one has a "father", Andre-Marie Ampere as does volts and ohms. Some measurements have very good reasons for why they are so named.

You've obviously never heard of Bernard Inch...

They may have a good reason for the name, but the magnitude is completely arbitary, usually based on convenience or other existing measurements or reference.
Del

Well yes and no - there is a well defined reasoned choice of the magnitude of this particular measurement, but it uses other measurements which if you dig far enough will lead to a totally arbitrary value having been chosen at an earlier time.

I thought the original post wanted a reason for the name, but you probably interpreted correctly and deduced the answer was to be why the magnitude was such.

Hey - you have to start somewhere when defining a new branch of science, which this was back in Ampere's time.

What is water? Why is it rated in gpm?

Because several gazillion coulombs per second is inconvenient.

See[for amp-ampere-definition]:

http://en.wikipedia.org/wiki/Ampere