What is the difference between E and a PROLOG system?

To put it succinctly, E is a theorem prover and PROLOG is a programming language. Although they both can solve a common subset of problems, there are some significant differences. E works in a bottom-up fashion, systematically generating consequences from the set of input clauses, until a contradiction (i.e. a proof) has been found. PROLOG uses SLD resolution to find a solution in a top-down depth-first fashion, and, consequently, is not complete, i.e. it can run forever although a solution exists.

Here is a list of the most important differences:

So what does the nickname mean?

Starting with E 0.22, each release version has received a nickname. This usually is the name of a tea (or the corresponding tea garden) which I drank a lot while programming the version. It's a celebration of the positive influence of tea on productivity.