It depends on the context:
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It means "a Mathematical Expression".
it means lowest common multiple. the opposite to it is hcf or highest common factor ^_^
Interpret, in math terms, means to explain something. You may see a problem that wants to you to "interpret" radicals or other mathematical data, but that just means you have to solve it, and provide the reasoning behind it.
it can either mean the number e raised as an exponent or it can mean just simply and exponent.
pi2r can be calculated, but is has no particular mathematical interpretation.