Micro-limit

From PokerWiki

The definition of micro-limit varies from one person to another, but generally extends from the lowest games offered to about $1/2 online. These stakes are impractical for all but the very largest brick-and-mortar rooms to spread.

Some people refer to the very smallest games, say 10c/20c and below, as nano-limit. Furthermore, although the term technically applies to fixed-limit games, some people also use it to refer to small stakes no-limit hold 'em.