Maintainer
A developer trusted to review other people's code and decide what gets accepted into a project many people rely on.
What it tells you about a developer
A maintainer has senior-shaped judgment by definition: they evaluate other people's code, say no diplomatically, and carry long-term responsibility. Maintainers also tend to interview candidates well, since reviewing strangers' code is their daily practice.
Maintainership is earned trust in the open source world. Maintainers sort bug reports, review submitted changes, and gate what ships into a project many people rely on. Nobody appoints themselves maintainer: the community extends that trust based on demonstrated judgment.