Definition of a situation 4 way
A 4 way or 4 way pot is said to be played at once when there were 4 players present. A 4 way pot can be played for several reasons. One of them is that all players have a very strong hand. It is also possible that the action was passive preflop. When one player limp and another decides to call, most of the time, the blinds (small and large blind ) will also call. Played 4 way situations will be quite rare unless you find yourself in the passive casino games.
A classic example of 4 way pot
A recreational and curious player limp in UTG position. The player on the button has a speculative hand (say 5-6 matching) and also decides to make a limp. The player on the small blind then has only a small amount to add to the pot to go see a flop and the player in the big blind position has already paid his blind and will go to see a default flop. So we know that the pot will be played for 4 way. In this type of situation, players will tend to play according to the strength of their hand and bluff little.