It's often called an indicator function. (The Kronecker delta is a special case of the more generally defined set-indicator function [0], the notation for which

It's often called an indicator function. (The Kronecker delta is a special case of the more generally defined set-indicator function [0], the notation for which is also more obvious. The Kronecker delta can be described in this notation as something like 1_{i=j}(i, j).) Similarly, the Dirac delta function is often more descriptively called an impulse function. The Heavyside step function does what it says on the box. A great many things in mathematics do have descriptive names, although it often helps to know a bit of Latin or Greek or to "get" the metaphor. That said, I don't think naming things in mathematics is particularly akin to naming things in programming. In programming, a good name can tell you enough about an object to be able to use it without understanding anything further about it, but in mathematics it's rare to be able to get much use from an object unless you assimilate its definition and the major consequences of its definition in the context you're working in. There are few "user-facing APIs" in mathematics, and mostly for good reason. 0. https://en.m.wikipedia.org/wiki/Indicator_function https://en.m.wikipedia.org/wiki/Indicator_function