There are generally 3 ways to earn (or retain) status - flying required miles, flying required number of sectors, paying enough. (Also 2 other ways - comp for those with status in another program, free status if considered by airline to be a VIP - eg heads of state, captain of industry.)

With some programs you dont need as much to retain as to earn in the first place.

With some programs there are lifetime status options.

With some programs if you dont requalify then you only drop one level (at others drop to whatever you earned).

Period of status can vary - some it is based on calendar year (with overlap to say Feb), others based on when you joined.

Some programs only have a couple of levels of status, while others have 3 or 4.