Did a little Google search and dug this up:
Channel Faders, Pre-fader Listen, and Channel On Switches
Smooth, noise-free 100-mm linear faders make it easy to set up the optimum balance between channels, while PFL (Pre-Fader Listen) switches allow convenient solo monitoring of a channel's pre-fader signal. All channels additionally feature channel on switches that can be used to switch the channel signal into or out of the mix without changing any other setting.
Carl