Concentric means "sharing the same center". Con- = used multiple times, -Centric = center-related. (like cooperate: multiple people doing the same task)
So, it's like a dartboard or bullseye: the circles are all around the same point.
Something three-dimensional, like cylinders (water bottles, spray cans), may be coaxial.
A place where a tyrranical goverment sends a group (or groups) of people that the leader/leaders of the tyrrany doesn't/don't like. Often times, it is a closed-off area that is surrounded by barbed-wire fences and search towers. The main reason that the tyrannical government sends these people to the camps is because they want them killed off because they think that that particular group of people is inferior or a danger to society. Not many people survive these camps.
This is a code word used in situations, such as in the presence of parents, when it is inappropriate to say the word 'semen'. Mostly used in place of the word 'come' to disguise the nature of the conversation.