Symbols:Abbreviations/W

WFF

 * Well-formed formula.

WRT

 * (Differentiation) with respect to.

When performing calculus operations, that is differentiation or integration, one needs to announce which variable one is "working with".

Thus the phrase with respect to is (implicitly or explicitly) part of every statement in calculus.

The abbreviation WRT or w.r.t. is frequently seen, and often pronounced something like wurt.