Topic maintainers are responsible for reviewing patches in the Drupal core issue list that are tagged "Needs TOPIC review", where TOPIC is the topic that they are maintaining. Examples of topics: Usability, Accessibility, Documentation

For more about these roles, see the Drupal core maintainers page; to see who currently holds these positions, see the core/MAINTAINERS.txt file in the latest development version of Drupal core.

Impact: 

Some aspects of the Drupal core project are system-wide and correspond to one of the core gates that all proposed changes must pass. Topic maintainers ensure that patches improve rather than cause regressions for these topics and help educate other contributors on how to do the same in their patches.

How to get started: 

Review issues in a topic area that interests you, and/or make patches or merge requests in that area. After participating in issues for a while, create a Drupal core issue asking to be made a topic maintainer. You will most likely be made a Provisional maintainer first, and after a term of 6 months, a full maintainer.

Skills required: 
Drupal site administration
Drupal site building
Using Git
Tasks this role performs: 
Review a patch or merge request