When I did some reading on the current situation, I found a lot of sites out of Australia that were repeating this "base load" idea, in the context of nuclear power.
I suspect that this is fossil-fuel propaganda.
Fossil fuel companies love promoting nuclear power because they know it takes decades to get a reactor built (if it gets built at all), and in the meantime, everyone keeps using fossil fuels.
It's the perfect way to cripple renewables without being obvious about it.