Org, as an Emacs mode, makes use of Elisp regular expressions for searching, matching and filtering. Elisp regular expressions have a somewhat different syntax then some common standards. Most notably, alternation is indicated using ‘\|’ and matching groups are denoted by ‘\(...\)’. For example the string ‘home\|work’ matches either ‘home’ or ‘work’.
For more information, see (emacs)Regular Expressions in Emacs.