Layouts
100%/104 key/108 key layout
The 100% layout will have all of the keys in a standard keyboard. 108 key keyboards will have four media keys above the number pad, resulting in a key count of 108. This layout is not recommended unless one makes use of the number pad, as the keyboard will take up a lot of space on the desk. Having to sacrifice space for mouse movements can be detrimental to gamers using a low sensitivity setting.
80%/87 key/TKL/SSK layout
The TKL layout, or the tenkeyless layout, is exactly as it sounds. It takes a 104 key layout, and takes out the number pad. This provides a large boost in desk real estate, allowing the user to have greater freedom for mouse movements. This layout was popularized by the IBM Space Saver K, which is why it is sometimes called the SSK layout. This layout is extremely popular in gaming keyboards.
60%/61 key/Pok3r/compact layout
The 61 key layout is quite compact, which is why it's sometimes referred to as the compact layout. Popularized by the Vortex Pok3r keyboard, it is sometimes referred to as the Pok3r layout. The layout is a TKL without the nav cluster, arrow keys, the function row, and the esc key. Through customizing the firmware, the user can still use the keys that are not present on the keyboard. Since a lot of keys are missing, this layout is recommended for gamers and those who travel with a keyboard. Those first trying the 60% layout may find the lack of arrow keys disturbing; Huskeyboards recommends mapping hjkl on layer 1 to arrow keys, with the spacebar acting as a layer key when held.
Miscellaneous Layouts
Many other layouts exist other than the ones listed above. The keyboard on the left, for example, is a 75% layout keyboard. It is essentially a 60% keyboard with an additional column, arrow keys, and the function row above the number row for maximum usability while still maintaining the compact nature of the 60% layout.