A synthetic polymer (a big molecule made of repeated units) that's used as a mild cleansing agent. It is also used in contact lens solutions and a regular on the ingredient lists of micellar cleansing waters.
Chemically speaking, it is an interesting molecule with an oil-loving part in the middle surrounded by two water-loving parts. The numbers in the molecule refer to the overall molecular size and the water-loving part in it (40%). Poloxamer 184 is almost half-half oil and water-soluble, likes to form micelles (molecules gathered into a ball form with oil-loving parts inside and water-loving parts outside) and is claimed to be an effective cleansing agent that is also mild on the skin and the eyes.
If you wanna know more about poloxamers, we have some more info at Poloxamer 407 >>