It is normal for cameras to have dead pixels. Generally, these are corrected by averaging the neighboring pixels to fill in a value for the missing pixel.
However, with the Sequoia, dead pixels are characterized at the factory and tagged in the image metadata so that processing software can determine the best way to handle those pixels.
Camera manufacturers perform defect testing to ensure that the number of dead pixels is not above a certain threshold. For the Sequoia, this threshold is less than 50 pixels. This means that out of 1.2 million pixels, the number of dead pixels must be less than 50 (or 0.0042% of the total pixels).