Blooming is a rare phenomenon you will see in some pictures, typically when shooting directly into the sun, because there is too much light/energy coming on a certain area of the sensor, saturating the pixels, and provoking a kind of overflow influencing the neighboring pixels.
Some sensors are less prone to blooming (my D200 exhibits less blooming than my D70 under the same circumstances) and the only remedy is to avoid those shots.
Here is an example of what it looks like: