If the math equation you're doing has letters or other symbols that stand for numbers, you're likely doing algebra. You probably took your first algebra class early in your high school years.
The noun algebra comes from Arabic word al jebr, meaning "reunion of broken parts," which appeared in the title of mathematician al-Khwarizmi's famous book on equations. In algebra you use basic arithmetic like addition and subtraction, but the quantities you're working with are often unknown — that's why they're represented by letters. You might remember solving algebra equations that look like this: a(b + c) = ab + ac. The letters a, b, and c all represent a number.