If there's a single common element that ties all action movies together, it's a universal preference for movement over dialogue or character development. Action movies revolve around action sequences. Very often, interludes of dialogue or plot development exist to link one action sequence with the next. The fast-paced sequences are the audience's pay off for going along for the ride.
Action movies have always been a popular genre. They reached a pinnacle of box-office supremacy in the 1980s. The careers of some of the industry's biggest names were built on the success of action movie franchises. Sylvester Stallone turned his Rocky and Rambo movies into a lengthy career. Arnold Schwarzenegger built a political career on the Terminator or Conan the Barbarian films. Bruce Willis, Tom Cruise and a host of other superstars have the action movie genre to thank for their livelihoods.
Action movies online are commonly part of the crime or military thriller genres. They can fall into other genres as long as the action in their story lines trumps inaction.