What does it mean when manufacturers point this out specifically in spec sheets?

It is actually the number of pixels that composes the photograph when you are viewing it. There is a part of the sensor's capture that is not actually seen or do not form the actual image.

AFAIK Effective pixels refer to the acual amount of pixels that is used to make up the image. the sensor itself may have more pixels but a portion remains unused for whatever reason. That is why effective pixels are always less than or equal to total pixels. :)

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Naunahan pala ako ni sir Nino. :D

Here (http://photonotes.org/cgi-bin/entry.pl?id=Effectivemegapixels) from GoogEarl! :) HTH

Thanks thanks :D