What is a predicate?

Question

Being a hobbyist coder, I'm lacking some fundamental knowledge. For the last couple days I've been reading some stuff and the word "predicate" keeps reappearing. I'd very much appreciate an explanation on the subject.

Answer 1

The definition of a predicate, which can be found online in various sources such as here, is:

A logical expression which evaluates to TRUE or FALSE, normally to direct the execution path in code.

Referencing: Software Testing. By Mathew Hayden

Answer 2

In programming, a predicate is a function which returns either true or false for some input.

Most commonly (I guess) used in the context of higher-order function. E.g. filter is a function in many languages which takes a predicate and a list as arguments, and returns the items in the list for which the predicate is true.

Example in javascript:

function lessThanTen(x) { return x < 10; } [1,7,15,22].filter(lessThanTen) --> [1,7] 

The function lessThanTen is the predicate here, which is applied to each item in the list.