I got a stupid math-question. I'm revisiting HS maths but I never think I got this when I was in school.

what does something like a^pi mean? where the exponent is an irrational number- or any exponent that can't be easily made into a rational number to make it an nth root- how many times would a be multiplied by itself? you can get it to a^3 * a^0.1415(etc) but then what does a^0.1415(etc) mean. How do you make sense of this?