A closure is a function. The function resultant value depends on the value of variable(s) declared outside the function.

We can use this small script by way of illustration:

var factor = 7
val multiplier = (i:Int) => i * factor
val a = multiplier(11)
val b = multiplier(12)

We define a function named multiplier. The function expects an Int argument. For each argument, we take the argument and multiply it by the external factor variable.

We see the following result:

Closures have a nice feel as they do what you expect with little fanfare.