E-mini
CME Group's electronically traded futures contracts at one-fifth the size of the original floor-traded standard contracts.
E-mini contracts were introduced by the CME in 1997 (starting with ES) to make index futures accessible to retail traders. They are exactly one-fifth the size of the original "big" contracts: ES = $50/pt (vs. SP = $250/pt), NQ = $20/pt (vs. ND = $100/pt).
E-minis trade entirely electronically on Globex, 23 hours a day, 5 days a week. They are now by far the most liquid equity index futures in the world — the "big" contracts still exist but have negligible volume.
The product family includes ES, NQ, YM, and RTY, each tracking a major US equity index.