Tux
Tux is the name of the penguin mascot used for the Linux kernel. Although initially created for the Linux kernel, Tux is used today to represent anything related to Linux, including Linux distros. The picture here is an example of Tux, originally drawn by Larry Ewing in 1996 using GIMP (GNU image manipulation program).
In 2009, Tuz, a Tasmanian devil wearing a fake penguin beak, was named the brand character for Linux kernel 2.6.29. The character was created to help promote the support effort to save the Tasmanian devil from extinction.
Since its creation, the penguin and name "Tux" has been used in games, software, and other parts of our culture. For example, Tux Paint is a paint program using "Tux" as part of its name. Many enthusiasts have also created variants of the Tux penguin. For example, a Slackware version of Tux is smoking a pipe and has a hair cowlick, and WSL (Windows Subsystem for Linux) has a friendlier penguin.
What is a penguinhead?
A penguinhead is another name for a Linux enthusiast or Linux geek.