equation means: two mathematical expressions that are separated by an equal sign. Usually, an equation has one or more unknown numbers. The unknown numbers are often called x, y or z. A solution is a value we can put in place of a letter that makes the equation true. True means that the left and the right side both give the same value. Example:

2 * x + 4 = 12

If we put 4 in place of the x the left side will evaluate to 12. So both the left and the right side become 12. The equation is then true and x=4 is therefore the solution.