a program that lets you edit files at a low-level basis

a program to manipulate binary files on a computer (as opposed to plain text)

a program which allows you to edit raw programs and data-files

a software program that works like a simple text editor but shows all the single bytes of your file

A hex editor (or binary file editor or byte editor) is a type of computer program that allows a user to manipulate binary (normally non-plain text) computer files. Hex editors that were designed to edit sector data from floppy or hard disks were sometimes called sector editors or disk editors.