UHMW is an abbreviation for Ultra High Molecular Weight, a kind of polyethelene plastic. Very lightweight (approx. 3/4 the weight of Lexan), it is quite durable. A common application is cutting boards - most white plastic cutting boards are made out of UHMW or a varient. Another application is as a lightweight bearing block, as UHMW has self-lubricating properties that make it a decent replacement for ball bearings, at least at lower RPMs.