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