What is the difference between defn and defmacro?

Question

What is the difference between defn and defmacro? What is the difference between a function and a macro?

Answer 1

The Other answers cover this well in depth so I'll try to cover it as succinctly as I can. I would appreciate edits/comments on how to write it more succinctly while keeping it clear:

• a function transforms values into other values.
  (reduce + (map inc [1 2 3])) => 9

• a macro transforms code into other code.
  (-> x a b c) => (c (b (a x))))