Tangential speech is a communication disorder

Communication disorder

A communication disorder is a speech and language disorder which refers to problems in communication and in related areas such as oral motor function. The delays and disorders can range from simple sound substitution to the inability to understand or use language...

 in which the train of thought of the speaker wanders and shows a lack of focus, never returning to the initial topic of the conversation.

Tangential speech is less severe than logorrhea and may be associated with the middle stage in dementia

Dementia

Dementia is a serious loss of cognitive ability in a previously unimpaired person, beyond what might be expected from normal aging...

. It is, however, more severe than circumstantial speech

Circumstantial speech

Circumstantial speech is a communication disorder in which the focus of a conversation drifts, but often comes back to the point...

 in which the speaker wanders, but eventually returns to the topic.

Some adults with right hemisphere brain damage

Right hemisphere brain damage

Right hemisphere brain damage, often abbreviated as RHD, is damage to the right hemisphere of the brain. It is associated with a number of cognitive and behavioral difficulties in humans. Research has for long focused on the effect and the role of RHD on emotional problems and in particular on...

may exhibit behavior that includes tangential speech.