Around the world, soccer (or football, for anyone outside the U.S.) reigns supreme as the most popular spectator sport. Every region, and almost every country, is crazy about "footy," and annual revenues for the soccer industry are just under $30 billion. Yet somehow, the sport has still not caught on the United States. Perhaps, it's because Major League Soccer (MLS) isn't quite on the same level as some of the more popular leagues around the world, but then again, maybe MLS lags behind due to the sport's low popularity. Whatever the answer, Americans just don't know very much about soccer. If you're from the U.S. and you're looking to improve your knowledge of the world's most popular sport, read the following guide to soccer lingo. Nutmeg This is one of the most entertaining slang terms in the sport of soccer. A nutmeg is a move where a player kicks the ball between the legs of a player on the other team. The origin of the word is unknown, but it could be an example of Cockney rhyming slang. "Nutmeg" rhymes with "leg", so some say that's where the word comes from. Header This term is fairly obvious, but it's a good one to know because it defines one of the more exciting plays in the game of soccer. A header happens when an attacker scores a goal by head-butting the ball into the net. Playing with the head is one technique that sets soccer apart from other sports, including the American "big three": football, baseball, and basketball. Bicycle Kick The legendary Brazilian soccer player Pele was famous for his bicycle kicks. A bicycle kick is when a player does a back-flip in order to kick the ball while he is upside down. This move allows the player to kick the ball in the opposite direction from the direction he was facing. Due to its difficulty, this move is pretty rare, but it's great to see when it happens. Cross Although this term isn't particularly exciting, it's important to know because it's used so often in the game of soccer. A cross happens when one player kicks the ball from near the side of the field toward the goal, and another player, who is near the goal box, plays the ball before it hits the ground. Headers and bicycle kicks are two common ways to play crosses. Corner A corner, or corner kick, is very important to understanding the game of soccer. A team is awarded a corner kick when the other team kicks the ball out of bounds on their own end of the field. Many soccer goals are the result of corner kicks, so defending teams must be careful about when they choose to kick the ball out of bounds. Handball or Handling Another important and unique term in soccer, handball is a type of penalty. Most people know that soccer players aren't allowed to touch the ball with their arms or hands, with the exception of the goalkeeper. Although many people assume that any contact with the hands is illegal in soccer, that is not quite accurate. Actually, only deliberate hand or arm contact is illegal. Of course, it's up to the referees to decide whether contact is deliberate or not. The importance of the referee's decisions is another unique element of the game of soccer. Although this list is far from comprehensive, knowing these terms will help new soccer fans in the U.S. to follow and enjoy this sport. After watching a few games, even Americans can come to understand the mega-popularity of association football.