Well, a seasonal beer is that has been brewed for a particular holiday, season or even festive period. If you had or had not noticed, most breweries produce a few seasonal beers. The seasonal beer is mostly produced when the fresh ingredient is readily available.
Let us see by season
During spring, Bock would be traditionally prepared in the winter to be consumed during Easter and Lent. Bock was also traditionally produced to be consumed during the winter.
The summer season beers are typically built to accommodate the warm weather, and for this, most are light bodied. Most could have some fruity or citrus flavor, which at times is accented with the use of some spices, honey and the floral hops. The summer season beers include the wheat ales.
The fall beers are incorporated with the use of various spices, such as nutmeg and cinnamon. Thus, it directly serves to associate the beer flavor with the current season. One the other hand, the species are cleverly used to create some frame of reference that is unique to the season.
Traditionally, the Bock beer was brewed at winter to be consumed both during the winter and spring season.
The winter warmers are the common types of beers that are created; they include the mild ales and the old ales that are brewed in the winter months. Just to have that extra flavor in the beer, the winter warmers could have some spices just for additional flavor. The Wassail-style beer has sometimes been described as one of the winter warmers.