In physical terms it’s called a dynamic weight transfer. Although your Centre of Gravity (and hence your mass) remains between the wheels, by either pumping hard or putting in a rapid hard pedal stroke, you can negate the turning moment around the rear wheel, ergo, the bike doesn’t immediately start to “nose dive”.
In high traction conditions, the pedal pump works well, and effectively the chain tension holds the front of the bike up. If it’s slippy, then you’ll probably need to use the pump technique, to preload your bike into the ground, and during the rebound, effectively reduce the weight on the front tyre to zero.
The key is the word “dynamic”, as this cannot be kept up indefinitely. To do that, you actually have to move your CofG to the middle of the contact patch of the rear tyre, a technique applied for a “Flat Land manual” where there is no pitching moment around the rear tyre and the bike can “unicycle” along continuously 😉