If you were looking for the game mechanic introduced in Generation V, see seasons.
A season of the Pokémon anime is a collection of dubbed episodes that begin airing for the first time over the course of a year starting between August and September (Seasons 1-9), between April and June (Seasons 10-13), or between January and February (Seasons 14-present). They usually share an opening, and are often 52 or fewer episodes long. There is no distinction between these dubbed seasons in the original Japanese airings, except when the seasons' beginnings and endings coincide with those of a new series in Japan. Each season also has a movie that corresponds to it, though the pairing of a movie with a specific anime season is merely due to the annual release they undergo in Japan.
It should be noted that these seasons do not apply to the Japanese version of the show, where episodes of Pokémon air nearly every Thursday. Previously, the English dub was aired on a schedule similar to most American shows, where each season is typically aired new for nine months out of the year, with three months (usually during the summer) taken off to begin production for the next season, during which reruns air. The Japanese release schedule, with an episode airing nearly every week, was eventually adopted by Pokémon USA (now known as The Pokémon Company International) after 4Kids Entertainment lost dubbing rights.
