The Stroop effect, in its classical form, is an effect found when attention-grabbing word meaning interferes with the naming of the ink the words are printed in. For example, if the word "red" is printed in the ink color green, then it is harder to name the ink color than if it had been printed in red (or black). It typically takes longer to name the ink color when it doesn't match the word meaning. One possible explanation of this effect is that the meaning of the word captures attention and thereby distracts us from the task we are supposed to carry out.
Figure 1: The word ‘red’ is here displayed in the color black (left) and the color green (right). It takes longer for subjects to name the color of the ink when the word is printed in green than when it is printed in black or red. Image credit: Berit Brogaard and Kristian Marlow.
The Stroop effect, or "Stroop-like effect," has been reported in many other cases. For example, studies indicate that words denoting body shapes may trigger a similar interference in people who are at risk of having an eating disorder (the effect reported in these studies remains controversial).