What does "calculus" mean in the most general sense? 
Possible Duplicate:
What do Algebra and Calculus mean? 

I understand that there is calculus, as in math 101 integration and differentiation. Then there is lambda calculus, and there is logical calculus, propositional calculus, etc. 
What does the general term "calculus" mean?
 A: I don't think there is really a most general sense; rather there are various different senses.
"Calculus" is Latin for "pebble".  The "-ul-" suffix indicates that it refers to something small.  In dentistry, "calculus" means mineral deposits in people's teeth.  Among modern senses of the word, maybe that one is closest to the original meaning.  The word "calculate" ultimately comes from the use of pebbles in abaci for calculating.  Various modern senses come from that.  When the word is used for the differential and integral calculus and also for the predicate calculus, they're two different meanings that evolved from the sense of calculating, not two instances of a general meaning.  Some things like "vector calculus" and "calculus of finite differences" evolved from the sense in which the word is used when it refers to differential and integral calculus.
Addendum several minutes later:
See Calculus (disambiguation).
A: From Wikipedia:

More generally, calculus (plural calculi) refers to any method or system of calculation guided by the symbolic manipulation of expressions.

I think the key word here is "calculation" which is further explained to mean manipulating symbols, not just numbers as the lay-person might define it.
A: Actually, the term is rather broadly used:

we start seeing a whole bunch of chemical weapons moving around or
  being utilized. That would change my calculus, that would change my
  equation 

(Recent statement by President Obama)
Opinion: Milton Friedman and the calculus of common sense
Netanyahu’s calculus
In these senses the usage appears to match the definition "A particular method or system of calculation or reasoning."  The mathematical definitions presumably derive from this, with each specific mathematical meaning being a separate "method or system".
