What does in between means for inequality?

Answer 1

It means that something is greater than some number, and smaller than some other number. For example, the solution of an inequality might state that "x" is greater than 0, and that "x" is also less than 10, in symbols:

x > 0 and x < 10

Which can be written in shorthand notation as:

0 < x < 10

Note that instead of "less than" and "greater than", you might also use "less-than-or-equal" and "greater-than-or-equal", or some combination. For example:

0 < x <= 10