Tangentiality is a speech disturbance characterized by digressing from one subject to another without ever reaching a conclusion. An individual with tangentiality will be asked a question or start out on a topic and using loose associations will begin discussing another topic and then another loosely associated subject with no conclusion or answer for the original topic. This is a symptom in bipolar disorder, schizophrenia, dementia, and other brain disorders.
For example, a person exhibiting tangentiality is asked what their absolute all-time favorite food is. The may being by saying how they really like apples and how that they prefer red apples to green ones. This could lead to the colors red and green and how they are typically associated with Christmas. Then they may start talking about how Christmas is a fun holiday. This may lead to a discussion about how holidays are fun because you get to spend time with friends and miss work and school. This may lead to a discussion about how work or school is going. This is tangentiality - the initial question about favorite food goes unanswered while different loosely related topics are brought up.