1. The act of pondering or thinking; meditation: Some people have psychological ruminations involving distressing thoughts for a very long time.

2. Persistent meditation on a subject, particularly thinking about and reviewing one's past: For some people, rumination is known to obsess them with a single idea, or set of thoughts, with the inability to get rid of them or to dislodge them from their minds.
3. In certain animals, the fast swallowing of food and then ejecting it and chewing it more thoroughly at a later time until digestion is completed in their other digestive areas: Cows and sheep are just two examples of animals that break down the vegetable matter that they eat by rumination.

A continuous focus on or brooding about memories, plans, or ideas; some of which are usually not serving any useful purpose: Janet was having obsessive ruminations for weeks before going on the reporting assignment the editor gave her regarding how well the U.S. military families were living in Germany because she had never been to a foreign country before.