This may seem like an odd phrase, because how can a number not be 'Real'?
But in fact it means a very specific type of number. Namely one that is not an integer i.e. a number that is allowed to have decimal points.
123 is an Integer
123.0 is a Real number
Real numbers are stored and handled in a computer using 'Floating Point' notation.
As an aside, there are also 'Imaginary Numbers' but only mathematicians and engineers tend to use those types of numbers.
See also 'Floating Point' in the glossary.
Challenge see if you can find out one extra fact on this topic that we haven't already told you
Click on this link: Real Number