At its 1986 Session in Lausanne, the IOC decided to introduce this change. From 1924 to 1992, the Summer and Winter Games were each held in the same year, every four years. This four years period is called "Olympiad". The last Summer and Winter Games held in the same year were in Barcelona (Summer) and Albertville (Winter) in 1992. Since then, the Summer and Winter Games are each still held every four years but the Summer Games are celebrated during the first year of an Olympiad and the Winter Games held in the third year.
Learn more:
Factsheet: The Games of the Olympiad
Factsheet: The Olympic Winter Games
Educational series: The Modern Olympic Games