Focus =Kendra/Sankendrak/NAbhyAntar केन्द्र संकेन्द्रक नाभ्यान्तर---------Focal length=Kendra Doorii,NAbhiya Doorii,Focus Doori केन्द्र दूरी, नाभीय दूरी, फोकस दूरी

The focus, or focal point of a lens or parabolic mirror is the point onto which collimated light parallel to the axis is focused. The focus of an elliptic mirror is either of two points such that light from one converges on the other. The focus of a hyperbolic mirror is either of two points such that light from one is reflected as if it came from the other. The distance from the lens or mirror surface to the focus is called the focal length.

focus=naabhi/kendra bindu नाभि/केन्द्रबिन्दु
focal lenth=naabhiya doori/kendriya doori नाभीय दूरी/केन्द्रीय दूरी

This is just a try to find out whether or not the concept can be grasped in another words than the routine ones.