Skirmishes are short, typically day long or less events, where people get together for basic airsoft fun. Games are quick with simple objectives or based on team elimination.
Operations are longer, often multiple day events, where teams must accomplish specific objectives. Operations are typically based on a schedule and can cover large operational areas. Operations can have multiple levels of complexity, and are objective based, rather than elimination type gameplay.
Milsim, or military simulation, is similar to a reenactment, except the weapons are airsoft replicas instead of actual firearms. Players must meet specific gear and uniform requirements, and gameplay mimics actual military units, locations, time periods, and tactics. Milsim is the most realistic, but also the most complex, form of airsoft.
In addition to the game styles listed above, airsoft is also very beneficial for training. This can include simple training to improve game related tactics and movements, all the way up to formal law enforcement and critical incident response training.