Binary or base 2 is the way that aliens with only 2 fingers count. I can imagine the face you are making in disbelief but in theory its true!
In general humans have 10 fingers.Since we have 10 fingers we count on a base 10 number system called decimal. We count from 0 to 9 and then start stacking numbers together. 10, 11, 12. . . . . .
A pattern begins to emerge from there. . . . 19, 20, 21,22, . . . . . 30, 31, 32,. . . . and we keep going on and on and on.
If for some reason we were a race of people with only two fingers total we would count much differently. We would count on a base 2 number system. We would count from 0 to 1 and then start stacking the numbers together. 0, 1, 10, . . . . . This base 2 number system is called binary.