Sliders are the part of a compound needle that is used to close the eye of the needle, lift loops off the needle during knitting, and move loops during transfers.
Sliders can also be used as temporary holding locations for loops transferred from the opposite bed. If a needle's slider is being used, the needle cannot perform regular knit operations since the slider will block it. Further, if a needle's slider is being used to hold yarn, no yarn carriers may be moved past the needle as they may impact the slider.
In knitout, sliders are referenced like as additional named beds with the names fs and bs.
One can use the xfer instruction to move loops to and from the sliders, e.g., xfer f5 bs5 to place loops from needle f5 onto the slider of needle b5.
Machines without sliders can use the half-gauge technique to emulate the functionality of sliders (at the cost of decreased gauge) by dedicating needles to act as temporary holding locations.