Titillation is material or behaviour which rouses sexual feelings without satisfying them. Satisfaction may come later. Then it's very pleasant. Satisfaction may not come. Then it can be pleasant but a bit frustrating. It can also be very frustrating depending on the situation. Considerate sexual partners do not intentionally rouse a partner without giving pleasant satisfaction.
To titillate can mean to get a person a bit excited and interested. It used to mean to touch a person gently or to tickle.