It is how to set the delay. 1/8 = eighth notes. 1/16 = sixteenth notes.
Measure of 4/4 time per measure = 4 1/4 (quarter) notes, 8 (eighth) 1/8 notes, subdivided further would be 16 1/16th notes.
Edge uses dotted eighth note settings a lot. A dotted eighth note is like an 1/8 note and a half. An eighth note being the same time span as 2/16th notes in length.
Making more sense? Easier to show than explain.
So a 3/16th would be dotted 1/8th note; spanning 3/16th note span.