right

From The K Language Wiki
Right
(:)

Right, a.k.a. dex (from Latin dexter), is a function that returns its rightmost argument.

 (:)[1;2]
2

When it accepts only one argument, it could be referred to as identity or identity function.

 (::)1
1

In some dialects the identity function could serve as a placeholder for missing indices in square-bracket indexing or for missing arguments in projections.