Per Wikipedia, in software development, "upstream" refers to a direction toward the original authors or maintainers of software.

See Surveying the mathematical software landscape

• Many of the packages in the SageMath distribution are upstream packages for the SageMath library.
• Used for the infrastructure:
  • Trac
  • Askbot
  • Google groups
  • GitHub
  • MoinMoin

• See task ticket #33774
• The Fedora people have a useful tool to track upstream version changes: https://release-monitoring.org/
• repology: sagemath_develop has much broader coverage.

Here are some useful trac queries (final "e" omitted on purpose to also get final "ing").

• summary contains upgrad
• summary contains updat
• summary contains upgrad or updat
• summary contains packag
• summary contains "upgrad" or "updat" or "packag"