Interference effects are a form of order effect that occur when the same person is subject to two different conditions, for example versions of software, during a within-subjects study. The user may in some way get used to the first condition (say A) and then become confused by the difference in the second one (say B) so that they perform less well than if they had performed B first.
This is the opposite of a learning effect.
Also used in hcistats2e: Chap. 3: page 34
Used in glossary entries: learning effects, within-subjects experiment