From PostgreSQL wiki
Contributor Listing Draft Policy
People to be listed on the PostgreSQL contributor listings include only people who have made substantial, long-term contributions of time to the PostgreSQL project. One-time only contributions are not usually considered adequate for listing, unless they involve quite large amounts of code and time. Financial contributions get listed on the Sponsors page (TBD), not here.
Listings will last, on average, two years before being re-evaluated. For this purpose, all listings will in the future contain information on what exactly the person contributed and when, although this information might not be displayed. Contributor listings will be updated at least once a year.
Editing the contributor listings will be carried out by the Core Team.
Core Team Section
This contains only the core team.
Major Contributor Section
This contains listings of contributors who have made substantial positive impact on the development of the PostgreSQL Community.
Contains listings of developers who have made smaller code contributions to the PostgreSQL project. Also lists people who have made large, sustained non-code contributions of their own time to the PostgreSQL project, within the last two years.
Lists people who were in the Major Developer or Contributor section, but have stopped contributing for two years or more.
Contains a listing of former core team members.