What is the real definition of DSLR?

[Ido]

The thing is CCD was the first digital sensor created in 1962. CMOS just perfected on it overtime ( mostly for photography).
Now DSLR vs mirrorless is a question mostly on ergonomics, as mirrorless are much compact. ( obviously technically, companies are trying to achieve standard quality, or in fact better than that as in case of leica). The most obvious quantity of difference in cameras that remains is of the viewfinder, and which lens supplies the image for it. The one taking the exposure(SLR or DSLR) , a different one dedicated to the viewfinder(TLR) , or none at all( mirrorless)

Well, there are also not-so-compact mirrorless system cameras, like the Panasomic Lumix DMC-GH4, and the new Samsung NX1. If one prefers a big handgrip and lots of room for spaced-out controls, there are still options in the mirrorless range.