Explain the difference between the expressions five is less than x and five less than x?

5 is less than x can be written as 5 < x and represents the set of all values of x such that 5 is less than x - or equivalently, all values of x that are greater than 5. This would comprise the part of that number line to the right of the number 5.

5 less than x is the expression x-5 and is the one value that is 5 units to the left of x on the number line.