Facial hair that all Unix experts are mysteriously compelled to grow. The length, bushiness, and unkemptness of the Unix beard are all directly proportional to the owner's expertise. Having a Unix beard is a great way to ensure that you never get laid.
Bob's a true Unix genius, just look at the size of his Unix beard!
It is the excuse hipster junior System Administrators use when they leave long beards. It is supposed to be measuring the level of expertise however it is really a ruse , a masquerade for them to satisfy their deeper hipster motivations. You can easily spot them when they compare their beard not with Tovald's but with the one Clooney has.
Dimitris clames he keeps his beard long to mark his UNIX expertise, calling it a UNIX beard. Hack through his browser history though, you'll see lots of Clooney images.