In GitLab itself, there are short definitions of feature (internal link) and bug (internal link) which are displayed when hovering over the labels. This page provides context and elaborates on these definitions.
GitLab's Iteration value means we often make small improvements to the product. We use this to get feedback on what features are important to people. It is not a bug when GitLab is missing functionality.
If we find that GitLab doesn't work as people expect, the documentation should be updated so this is no longer a surprise. This applies whether we classify it as a feature request or a bug.
Link back to the issue so it's easy to find out more details, workarounds, to see what progress we're making, and to contribute.
Bug issues report undesirable or incorrect behavior, such as:
Feature issues identify work to support the implementation of a feature and/or results in an improvement in the user experience.
If people care about a missing feature, then ideally the issue should be marked as
~"Accepting merge requests"