A season is the period of time in which football clubs in a nation play their competetive fixtures. Most countries run a Winter Season but some run a Summer Season. Most seasons last between 9 and 10 months
Most countries use a Winter season because most International tournaments are played during the summer, so fixtures would not be interupted. A Winter season is basically a seaso that starts one side of winter (usually August/September) and plays during the winter weather into spring, usually into May/April. Nearly all countries use this type of season and so does most intercontinental competitions such as the European Champion's Cup. The players have a break at the end of the season and report for pre-season training preparation usually in June or at the beginning of July. They usually have a large transfer window in the summer and a one-month window in January.
Some countries, like America, Ireland and Russia will start after the Winter months and play until September or October. While some do this through choice Russia is forced to due to the bad winter. They hold their off-season and pre-season during winter and usually have larger winter transfer windows than the one month transfer window seen in Winter Seasons. They usually have a large summer window as well, to maximise trading time with clubs that run a Winter Season.