Range is the corresponding value of a function which derives its value from the domain.
In simpler terms it would be analagous to the y value in a equation which has x and y.
example: y=3x+2 This could also be written as f(x)=3x+2
The range of this example would be all real numbers.
If we were to look at f(x)=1/(x+2), the range would be all real numbers except x=-2 (this would be undefined).
Range can also be defined as a set. The numbers do not need to be continuous.
In short we could say that the range is the y value or the f(x) (this is not always the case) but to be precise we could say the range are the value(s) that correspond to given numbers in the domain.