PET stands for Polyethylene terephthalate, it's the most common type of thermoplastic polymer resin of the polyester family and is used in fibres for clothing, containers for liquids and foods.
It's not actually fun but it's an important fact nonetheless
PET bottle generates more than 100 times the toxic emissions to air and water than making the same size bottle out of glass. In addition to that, producing plastic bottles may be harzadous for workers, there are many reported accidents that included explosions, chemical fires, chemical spills, and clouds of toxic vapor.
Sources: Wikipedia & Ecology Center