What does a megapixel designation on a lens actually mean?

I know that in a CMOS sensor the megapixels give you an idea of how many pixels are actually there to capture the light. In terms of a lens however, I cannot find any relation between the megapixels of a lens and that of the CMOS sensor. I agree that sensor size is important and that all light should fall on the active area of the lens. And I get 1/3 inch lens, 1/2.5 inch and so on. But I see many lenses which say 2 mega pixel lens on them (like in this aliexpress listing). What does this actually mean?

Answer

Both Samsung and Edmund Optics use the name "Megapixel" or "MegaPixel" to describe lenses they sell for C-mount and CS-mount cameras, but in both cases the term is used like a brand name rather than a description of any technical aspect of the lens.

There's also a perceptual megapixel concept developed by DxOMark to describe lens sharpness in a way that's supposed to be more accessible than traditional MTF charts. As far as I can tell, this "P-MPix" rating hasn't really caught on yet even though it was introduced a few years ago.

The example you cited is a very small, very cheap (under $6!) lens meant for a closed-circuit TV camera. It's hard to tell exactly what the "3 mega pixel" descriptor really means, and in fact it may not mean much of anything. It may mean that the lens is sharp enough to work with 3MP sensors, or that it's sufficiently unsharp enough that you shouldn't use it with anything better than a 3MP sensor.