Dispersal patterns or spread patterns were preset dispersal spreads used when firing torpedoes.
In 2366, in an alternate timeline, USS Enterprise-D weakened the deflector shields of an attacking Klingon K'vort-class warship by using dispersal pattern Sierra. The dispersal pattern involved launching five photon torpedoes simultaneously. The torpedoes spread out mid-flight and struck the target nearly simultaneously from multiple angles. (TNG: "Yesterday's Enterprise")
In 2370, when testing new photon torpedoes with a targeting system enhanced by Worf, the Enterprise-D fired torpedoes at coordinates 005-mark-317 of an asteroid field in spread pattern Delta 9-4. The spread pattern involved the rapid firing of three torpedoes: the first striking a central asteroid, the second an asteroid to the right, and the third an asteroid to the left. During the test, the third torpedo malfunctioned and missed its target. (TNG: "Genesis")