natural numbers = 1,2,3,4... symbol is N
whole numbers = 0,1,2,3... symbol is W
integers = -2,-1,0,1 symbol is Z
rational numbers = 0, 1/4, 1/2, 1, 2 symbol is Q
irrational numbers = numbers that cannot be expressed as fractions (sqrts, pi)
real numbers = the set of rational and irrational numbers together form the set of real numbers. stymbol is R