What is the difference between a concentration camp and an extermination camp as utilized by the NAZI's in WWII?

There is often very little difference between the two, and
frequently concentration camps over time turn into extermination camps.  Semantically
speaking, a concentration camp is a compound set up by a government in which person's
who meet a set of criteria are sent to.  They got their name because they are a
concentration of people who share something in common.  They are typically based on race
or political affiliation and they are started when that race or political affiliation
feels like a threat to a large portion of a population.  Concentration camps are meant
to separate these people from society in general.  Living conditions are usually
extremely sub-par, and residents are not in-frequently abused within their walls. 
Herein lies the main difference between a concentration camp and an extermination camp. 
Semantically speaking, no-one is to be killed at a concentration camp, they are just to
be kept separate.  At an extermination cam however, the purpose is to commit the mass
murder of a population of people that society feels threatened by.  Extermination camp
is a colloquial term that refers to the "concentration camps" for Jews in Nazi Germany
where people literally went to die.