The Bomb Spread is a technique that allows five Bombs to be created at once, which will spread symmetrically out of Samus.
It is possible to retain the charge while morphed by holding down after morphing. The shot button also needs to be held, as releasing it will cancel the charge. Releasing down will create the bombs, and the longer the charge is held before down is released, the higher the bombs will bounce upon creation. If the jump button is pressed instead, Samus will unmorph, retaining the original charge.
Note that this technique will not work if Power Bombs are selected, or if there are already Bombs or a Power Bomb on the screen.
Aerial Bomb Spread
Without involving a walljump, executing this technique while in the air requires turning around while facing down and pressing down to morph on the last frame of the turnaround animation.
The above can instead be performed by performing a walljump (while still maintaining the charge, so the shot button will have to be released before the walljump occurs) and, without turning around and before peak height from the walljump has been reached, pressing down while repressing the shot button, then releasing down after Samus has morphed.
Normally, the bomb spread is not a very useful technique; however, it can be useful in a handful of specific places, perhaps the most notable being the Red Keyhunter Shaft.