commit
The commit messages and authorship information will be scanned for the given string.
grep
All files in the currently selected tree (HEAD unless you are explicitly browsing a different one) are searched for the given regular expression (POSIX extended) and the matches are listed. On large trees, this search can take a while and put some strain on the server, so please use it with some consideration.
author
Name and e-mail of the change author and date of birth of the patch will be scanned for the given string.
committer
Name and e-mail of the committer and date of commit will be scanned for the given string.
pickaxe
All commits that caused the string to appear or disappear from any file (changes that added, removed or "modified" the string) will be listed. This search can take a while and takes a lot of strain on the server, so please use it wisely.