What is "σ" in a context free grammar? I have a grammar like this:

A → BAB | B | ε
B → 00σ | ε


What is the meaning of σ in the second rule?
Most probably, it means “for each letter $\sigma$ from alphabet $\Sigma$”.

If $\Sigma = \{ 0, 1 \}$, then B → 000 | 001 | ε.