x in algebra often stands for an unknown quantity, such as 2x+3=7.
x and y coordinates are used to describe equations.
When placed between two numbers like 2 x 4 it often means to multiply.
In carpentry 2 x 4 refers to a piece of wood that (before drying) measures 2" by 4". After drying it measures 1 5/8 by 3 5/8.