What does this mean in the definition of CW complex?

Question

On wikipedia, in the definition of CW complex, it states that

A subset of X is closed if and only if it meets the closure of each cell in a closed set.

What does this mean? I don't need an intuitive explanation or anything, I just literally don't know what it means. Does "meet" mean their intersection is nonempty? And "a closed set", what does that refer to? Literally an arbitrary closed set?

Answer 1

It means that a subset $C\subseteq X$ is closed if and only if $C\cap e$ is closed for any closed cell $e$. Note that the notion of "closed cell" (as in image of glueing map) and "closure of (open) cell" coincide.

Answer 2

$K$ is closed if for each cell $e_k$, we have $K \cap \overline{e_k}$ is closed.