Phoria, is a misalignment of the eye that is not apparent when the two eyes are in use. It appears when binocular vision is broken. This differs from tropia which is always present and obvious to an observer. Phoria is also known as latent deviation.
To test for phoria, your eye doctor performs a cover (and uncover) test. During this test, the doctor covers and uncovers your eyes alternately and observes them for movement. If any of the eyes move when it is being uncovered, that eye has a phoria.