The Commit bit is permission

Permission

Permission, in philosophy, is the attribute of a person whose performance of a specific action, otherwise ethically wrong or dubious, would thereby involve no ethical fault. The term "permission" is more commonly used to refer to consent...

 to contribute to a shared source code

Source code

In computer science, source code is text written using the format and syntax of the programming language that it is being written in. Such a language is specially designed to facilitate the work of computer programmers, who specify the actions to be performed by a computer mostly by writing source...

 for a software project.

To contribute source code on most large projects, one must make modifications and then "commit" those changes to a central repository such as CVS

Concurrent Versions System

The Concurrent Versions System , also known as the Concurrent Versioning System, is a client-server free software revision control system in the field of software development. Version control system software keeps track of all work and all changes in a set of files, and allows several developers ...

. To have "a commit bit" on one's user account means that one is permitted to commit those changes. This dates to the use of a literal binary digit to represent yes-or-no privileges in many software system

Software system

A software system is a system based on software forming part of a computer system . The term "software system" is often used as a synonym of computer program or software; is related to the application of systems theory approaches in software engineering context and are used to study large and...

s.