(adj) Of, relating to, or constituting a vestige; remaining as a trace of something that once existed but is no longer functional or necessary.

The appendix is a vestigial organ in humans, serving no apparent purpose in modern physiology.

Originally from Latin vestigium meaning “footprint” or “trace,” the term became prominent in evolutionary biology to describe organs or structures that have lost their original function through evolution.

Examples:

• <blink />
• gets()
• Windows Registry entries for Internet Explorer
• /etc/motd
• Adobe Flash Player plugin support
• TERM=vt100
• Serial port configuration utilities on modern laptops
• net send
• Javascript var