Code
regex
(abc) capturing group
(?:abc) non-capturing group
(a)(b)(c) groups 1, 2, 3
(?P<name>\w+) named group (Python/PCRE)
(?<word>\w+) named group (.NET/Java/JS)
(?<word>\w+)\k<word> named backreference
\g<1> backref to group 1 (Python)