Bioload means waste producing animals, for the most part fish. Reducing the bioload in most cases means reducing the number of fish in the tank. Sometimes it can be from animals that need constant feeding like non photosynthetic corals.
Too many feedings or overfeeding taxes the biofilter and must be compensated by increased water changes and the volume of each water change. That does not work with overstocked tanks though.
Cheers
Steve