Summer time in Europe is the variation of standard clock time that is applied in most European countries (apart from Iceland, Belarus, Turkey, Georgia and Russia) in the period between spring and autumn, during which clocks are advanced by one hour from the time observed in the rest of the year, with a view to making the most efficient use of seasonal daylight. It corresponds to the notion and practice of daylight saving time (DST) to be found in many other parts of the world. Summer time lasts 30 weeks in years when the last Sunday in March is after the 28th; otherwise, it is 31 weeks.