One of the natural periods into which the year is divided by the equinoxes and solstices or atmospheric conditions WordNet 3.0 & Open English WordNet

A season is a division of the year based on changes in weather, ecology, and the number of daylight hours in a given region. Wikipedia

One of the major divisions of the year. Wikipedia Disambiguation

Weather- or climate-based subdivision of the year Wikidata

One of the four equal periods into which the year is divided by the equinoxes and solstices, resulting from the apparent movement of the sun north and south of the equator during the course of the earth's orbit around it. These periods (spring, summer, autumn and winter) have their characteristic weather conditions in different regions, and occur at opposite times of the year in the N and S hemispheres. OmegaWiki

Each of the four divisions of a year: spring, summer, autumn (fall) and winter. Wiktionary