How do you say lab in spanish?

Typically, the correct answer is 'ciencia.' This refers to the study of sciences, like Biology, chemistry, etc. However if you're talking about science as an academic subject (as in going to science class), you would say 'ciencias.'

For a sentence like 'I have mastered the science of making money' you would use 'el arte' instead of 'ciencia' because science in that sentence refers to a knowledge of a system.