Calculus III But doesn't require Calculus :)

For my calculus III class, we began with elementary study of three dimensional vector equations.

One exercise asks for the domain of r(t) = e^(t)i + t(-1)j + (t+1)^(-3)k

I know the answer is t ≠ 0 or -1. However, when I looked the answer up, it was given like so: D = {t ∈ R, t ≠ 0, t≠ -1}

What does t ∈ R do? Specifically, what is ∈? Because I know t is a parametrized variable and R refers to the function of those parts.

Does it mean "for whenever R is parametrized with t, the domain is ..."?