A series is the recurring competition — the name riders recognise year after year. A season is one edition of it, usually a calendar year (some seasons cross New Year's Eve and carry two year labels).
Each season has its own rounds, its own standings, and — on the organiser side — its own scoring rules. A season can follow another season's rules exactly ("same rules as"), or carry its own. Comparing two seasons shows the rules delta and how riders moved between the two seasons' standings — see a series' compare seasons link.