Latex is a class of polymer which can be either natural or synthetic.
Natural latex can cause allergies for a rather high proportion of the population, especially medical workers (see latex allergy article).
Natural latex is derived from the sap of the rubber tree, a tropical plant originating in the Amazon (and now grown widely in tropical climates including Malaysia, Indonesia and India).
Latex is used to manufacture rubber, including gloves, condoms, car parts, elastic bands etc.