the variable represents any number that the P could be
There could be a variable in the numerator which is not defined. For example, [tan(x)]/3 has no variable in the denominator but the expression is not defined for x = pi/2, for example (90 deg).
n - 8 is the expression for the difference of eight and a number.'Number' is a variable, so the variable must be a letter (in this case, 'n'). 'The difference' is going to be the subtraction symbol that is in between the 'number' and eight, so it must be n - 8. It could, of course, be 8 - n.
With no context it is difficult to be sure but I suggest that n is a counter: a variable that goes 1, 2, 3, 4, ...and x, unfortunately, represents multiplication. I say unfortunately because the accepted symbol nowadays is * rather than x.So the expression is to multiply a number by its predecessor. The expression could represent the number of permutations of two objects selected from n distinct objects.
-27 is a number. Through the Reflexive Property of Algebra, -27=-27. You could also represent it as an expression such as 0-27 or -28+1.
It could represent an unknown variable in an expression or an equation.
No, it could be a qualitative variable.
the variable represents any number that the P could be
It could be: 21n2-4
That could be a 'coefficient'.
It could represent a vector.
3.5 M Molarity is moles per liter. An expression of concentration in 3.5 M.
It could be: 7(5x-3)
Could represent a vector P. Or the average (mean value) of a variable P.
There could be a variable in the numerator which is not defined. For example, [tan(x)]/3 has no variable in the denominator but the expression is not defined for x = pi/2, for example (90 deg).
Typically m is used to represent Mass; though, as it is a variable, m could be used for anything.
While quite a specific noun, idiom could have the synonyms phrase, expression, saying, dialect, or slang.