MVEL is a scripting language, but it is a superset of Java, so any Java expression is also an MVEL expression. Though you can do more with MVEL, e.g.
myVariable = myPerson.name
(which would be equivalent to myVariable = myPerson.getName())
You can check out the MVEL documentation for all details:
http://mvel.codehaus.org/
Regarding context or kcontext, they resolve to the same object, context was the old name we used first, we later switched to kcontext (which is now the preferred) as it is similar to ksession and kbase etc.
Kris