Sure, the square brackets in posix regex (used by grep) are for character ranges. You can wrap any single character in the brackets and it works the same.
So foob[a]r matches the literal string foobar. If you grepped foob[ab]r it would match both literal strings foobar and foobbr. However, it doesn't match the literal string foob[a]r because [] is a character range. To match that, you'd need to escape it something like foob\[a\]r, which would not match the literal string foobar. This is why you don't need grep -v grep
Understanding how and why this works will dramatically help you slice and dice text strings in a shell, so it makes a great SysAdmin interview question.
So foob[a]r matches the literal string foobar. If you grepped foob[ab]r it would match both literal strings foobar and foobbr. However, it doesn't match the literal string foob[a]r because [] is a character range. To match that, you'd need to escape it something like foob\[a\]r, which would not match the literal string foobar. This is why you don't need grep -v grep
Understanding how and why this works will dramatically help you slice and dice text strings in a shell, so it makes a great SysAdmin interview question.