What is "filar"

Filar \Fi"lar\, a. [L. filum a thread.] Of or pertaining to a thread or line; characterized by threads stretched across the field of view; as, a filar microscope; a filar micrometer.

a. Of or relating to a thread or line; characterized by threads stretched across the field of view.

adj. related to or having filaments especially across a field of view; "afilar eyepiece"