As an example someone is adding two additional rooms to a house. They finish the first room, but before they can start building the second -- they need to schedule an inspection, file paperwork, pick up supplies, etc.
In a sentence:
Before we can continue construction, we have some ????? tasks to do.
Construction is the main task, however these other smaller but necessary tasks must happen before construction can resume.
"Interim tasks" almost works, but doesn't emphasize that these tasks must be done before progress can continue. "Blocker tasks" also kind of works, but seems to imply that these smaller tasks are problems that were unexpected despite being predictable from the start.