Bottom fermentation is a process used in brewing beer, where yeast ferments at cooler temperatures and settles to the bottom of the fermentation tank. There are several synonyms for this term, including lagering, cold fermentation, and maturation. Lagering refers to the process of storing beer at cool temperatures for an extended period to improve its flavor and clarity. Cold fermentation is a more general term that describes any fermentation process that occurs at low temperatures and can include both top and bottom fermentation. Maturation refers to the process of allowing beer to age or mature, which can occur during or after fermentation. All of these terms describe the same basic process of brewing beer, but they may be used interchangeably depending on the context.