Antifreeze technically means a substance that does not freeze.  It is most commonly used to described three chemical solutions:  methanol, which is found in window washer fluids and is more toxic to humans and primates than dogs, ethylene glycol, the most toxicof the three types of antifreezes which is found in radiators and used as an antrifreeze in the cold months and as an engine coolant in warmer months, and propylene glycol, which is considered a safer but not but not necessarily non toxic form of antifreeze solution.  Propylene glycol is also found in small amounts in make ups and some medicines and food items.  

Ethylene glycol is the most dangerous  and the most common form of antifreeze used in North America.  Although many people consider it to have a pleasant taste, animals may drink it when there is no other water sources and unfortunately, only a small amount can be deadly.  After an animal ingests antifreeze, it is metabolized in the body and causes the animal to have a drunken appearance at first.  Eventually, it causes kidney failure through the formation of crystals that damage the kidneys.  While there is treatment that can be given to a pet that ingests ethylene glycol antifreeze, treatment must be given as soon as possible for the animal to survive.  In other words it is crucial that a pet that ingests antifreeze be treated by a veterinarian  immediately.