A "lite" denotes each individual framed glass unit within a window or door. Meanwhile, a "mullion" represents the separating line within a window or door, which can take on either a tangible or simulated form.
In the case of True Divided Lites (TDL), the window glass consists of multiple separate pieces, each divided by mullions that penetrate through the glass.
Conversely, in Simulated Divided Lites (SDL), the glass remains a single, substantial piece, with mullions positioned atop it, though they do not penetrate or intersect with the glass itself.
