A(n) is an abbreviation for the name of an element and has either one or two letters.
1.) atomic mass
2.) chemical symbol
3.) nuclear fusion
4.) periodic table
5.) group
6.) plasma

This is refered to as the chemical symbol. It is derived from the Latin name for the element which is why some elements like potassium (K) and sodium (N) have symbols different from their name on the periodic table.

It would be the equator.