"In the context of big-O notation, "complexity" has a meaning very different
from its everyday meaning. It basically means "scaleability" - how does the
time taken by the task vary with the size of the input? It's a rather
unfortunate choice of term. In particular, it has nothing to do with either
the human understandability of the expression, or the sophistication of the
internal implementation."

- Michael Kay

[Roger: That is the most beautiful description of complexity and the big-O
notation that I have ever seen]