confound refers to any factor occurring in a study that makes the results uninterpretable because its effects cannot be separated from those of the variables being studied.
Other /More definition:
Confound refers to an uncontrolled variable that affects our dependent variable. Confound is also called a Confounding variable.
It refers to any factor occurring in a study that makes the results uninterpretable because its effects cannot be separated from those of the variables being studied; situation in which extraneous variables are not controlled or cannot be shown to exist equally in one's experimental and control groups. When there is a confound, one cannot attribute changes in the dependent variable to the manipulation of the independent variable.