Selective inattention is a prolonged or chronic lack of registering or perceiving a particular stimuli. Typically the stimuli being disregarded is unpleasant, anxiety inducing, distressing, or deemed unimportant. An individual exhibiting selective inattention is ignoring and not registering the particular stimuli in order to avoid the mental distress that it may cause.
An example would be an alcoholic who is experiencing selective inattention in regards to the social and physical problems they are experiencing as a result of their alcohol consumption. Selective inattention is preventing them from perceiving the damage they are doing to themselves and others which would be mentally distressing. This is the opposing concept to selective attention.