The outer product quick þ can be attached to dyads and causes the dyad to act on each pair of elements in its left and right arguments. It is shorthand for €Ð€. For example if we had the code [1,2]+€Ð€[0,10] we could shorten it to [1,2]+þ[0,10] and they would both yield [[1,2],[11,12]]. I will refer to a dyad with þ applied (such as +þ) as an outer product dyad.
When an integer is one of the arguments of an outer product dyad, Jelly takes the range of that number first then uses the result as the argument. Knowing this, the above example can be further shortened to 2+þ[0,10]. This is true for both the left and right arguments of an outer product dyad.
Some outer product dyads when acting monadically on an integer yield certain integer matrices that can be useful in golfing (especially ASCII art challenges) but would take many bytes to otherwise construct. For example =þ when applied to an integer n yields an n×n identity matrix. [Try =þ onli