Active region

Active region may refer to:

• An unstable object (e.g. R-pentomino or century); a chaotic object; a relatively small, compact, isolated / well-separated part of a pattern or part of a reaction
• Any (not necessarily isolated / well-separated) part of an active reaction located within a particular region in the universe
• An active reaction or a specific generation of an active reaction

Also see

• Evolutionary sequence
• Engine
• Soup
• Index fossil