The word chess is derived from the Persian "shah," which means king. The board was developed between the third and sixth centuries in India and is comprised of 64 small squares. Only two players can play against each other, using 16 pieces each. The aim is to checkmate your opponent by threatening their king in such a way that it cannot escape or be freed by another piece in the next move.

Go originated in China, but was largely developed in Korea and Japan. It's played with black and white stones on a board crisscrossed by 19 horizontal and 19 vertical lines. Stones are placed on the intersections of the lines, with the aim being not to eliminate your opponent but to capture a majority of the board.

This Japanese variation of chess is played on a board divided into nine fields, though smaller or larger boards are also common. There's one important difference between shogi and chess: In the Japanese version, pieces are not assigned to a particular player, but can be used by both. Checkmate, however, is still the aim of the game.

A checkers board looks like a chessboard, but the rules differ greatly. In this case, players can only move their pieces diagonally across the darker squares, one square at a time, until they are able to capture their opponent's piece by jumping over it. The winner is the first to steal all of the other player's pieces. Checkers is also known as draughts and is called "Dame" ("lady") in German.

The board consists of three squares of gradually smaller size drawn within each other. Two players participate with nine tiles each. The aim is to get three of the tiles in a row, known as a mill, which allows you to remove one of your opponent's tiles. The winner is the first to reduce his opponent to two tiles, thereby hindering a three-tile mill.

It's perhaps the best game for long car trips, because all you need is a pencil and piece of paper. Tic-tac-toe dates back to the 12th century. Two players alternate in drawing an X or an O on a nine-square grid. The first player to create a row - horizontally, vertically or diagonally - wins. Tic-tac-toe was one of the first strategy games played on computers.

It's also considered a board game - but it's played vertically. "Connect Four" was introduced in 1974 and is a game for two players. The first to get four tiles of their color in a row - vertically, horizontally or diagonally - wins. It's similar to tic-tac-toe, except there are 42 open squares instead of just nine.

Initially conceived as a board game, "Civilization" was introduced in 1980. The idea was complex: A civilization must survive hardships from antiquity to the Iron Age. Seven players can play simultaneously and one game can last up to 10 hours. In 1991, "Civilization" was launched as a computer game and became an international hit.

Another favorite resource-related game is "Anno," introduced in 1998. The idea behind it is to discover and populate fictional islands and then meet the needs of the new island residents. It's also possible for players to compete against each other - simulating attacks and trade.

For some it may be a simple diversion, but in South Korea "StarCraft" is a national pastime. The real-time strategy game was introduced in 1998 and has remained one of the most popular computer games on the market. Player build a base, collect resources and acquire soldiers to fight their opponents. Online tournaments are of national importance in South Korea - and even open to spectators.

"Iron Mike" Webster won four Super Bowls as a center for the Pittsburgh Steelers in the 1970s. However, after his career ended, the many hits to the head that he had received as a football player took their toll on his health. He died in 2002 at the age of just 50. After his death, Webster was diagnosed as having had chronic traumatic encephalopathy (CTE), a neurodegenerative disease.

Bennet Omalu, a forensic neuropathologist (pictured above, second from left) was the first to diagnose CTE in Webster and other former NFL players. He continued his research despite widespread and strong resistance to his findings. In 2015 director Peter Landesmann (above, right) directed the film "Concussion," in which actor Will Smith (left) played Omalu.

Symptoms such as loss of speech, depression and dementia, which can be an indication of CTE, were first observed in boxers decades ago. Repeated blows to the head release the tau protein which accumulates in the brain. Those affected can experience changes to their personality, problems with aggression and even become susceptible to thoughts of suicide.

Between 2008 and 2015 Terry Long, Tom McHale, Jovan Belcher, Adrian Robinson and Junior Seau were among the former NFL players who committed suicide. In 2011, Dave Duerson, a former safety, shot himself through the heart instead of in the head. In his suicide note he asked that his brain be examined to see if he had CTE. Doctors found clear signs that he had had the disease.

Head injuries occur in soccer as well. In the final of the 2014 World Cup in Rio de Janeiro, German midfielder Christoph Kramer was knocked out. He soldiered on for 14 minutes after the injury, which was a big risk, because a second hit shortly afterwards increases the danger of long-term damage. Even now, there is no universally agreed procedure for diagnosing brain injuries on the sidelines.

Brain injuries in soccer tend to occur when two players clash heads when going for ball or as the result of an elbow to the head. A recent study by the Federal Institute of Sports Sciences has found that the risk of head injury in soccer varies according to a player's position. Defenders are most at risk, followed by midfielders and strikers. The risk is by far the lowest for goalkeepers.

A study conducted by the Federal Institute for Sports Sciences, showed that rugby players are at the highest risk among athletes of suffering concussion. They are followed by American football players, ice hockey players and basketball players. Brain injuries are not as common in soccer, but in Germany, where it is the biggest sport, in absolute terms, it is where the most concussions occur.