In Debian, maintainers are people who work on uploaded packages. There are :
Debian Maintainers (DM) :: Debian Maintainer is an official status of people, who are allowed to upload specific packages (with a DM field set). They don't need to request for sponsorship.
Here is a list of expressions which use the word "maintainer" :
Debian New Maintainer :: The Debian New Maintainers process, is the process of becoming an official Debian Developer (DD).
Debian New Maintainers' Guide :: The Debian New Maintainers' Guide is the first document to read if you want to work with packages.