it means the Solar "constant" is not constant
The Sun is a roiling mass of plasma. Like a boiling pan, it has multiple modes and scales of convection that are almost but not quite random. It fluctuates and flickers, slightly, as it boils and bubbles.
We, on Earth, feel the effects of this.
Maunder Minimum -> Little Ice Age.
"Global Warming"?
it does NOT mean that nuclear processes are varying, only that convection is by its very nature chaotic and inconstant. Luckily for life on Earth, it's only a LITLE bit inconstant...