A Small Club is a class of bidding systems in contract bridge where 1♣ is forcing and artificial but not necessarily strong.
Examples of small club systems are...
Polish Club
Roman Club
SAYC+ Where one level openings have all the same meaning as Standard American Yellow Card but the strong 2♣ opening is superimposed on the 1♣ opening. This free up the two level bids for other purposes.
References
Small club system Wikipedia(Text) CC BY-SA