Coal and nuclear plants have poor abilities to ramp power production up and down in response to fluctuating demand, so they were called 'baseload'. Various versions of natural gas power plants could respond more rapidly, so they were typically placed in the other other two categories.

This is all irrelevant if you have distributed wind/solar production coupled to efficient storage systems that manage the distribution using technology that doesn't have those limitations. Practically that means short term storage of power in batteries (daily), long-term storage in synthetic fuels (seasonal).