What is "binary-safe"

Binary-safe is a term mainly used in the PHP programming-language to describe expected behaviour when passing binary-data into functions whose main responsibility is text & string manipulating.

A binary-safe function is essentially one that treats its input as a raw stream of bytes and ignores every textual aspect it may have. It would therefore be more correct to characterize a 'binary-safe' text-function as one which incidentally works on text, but whose primary mode of operation is on raw binary data.