Tricks, Techniques and Ideas

We use a variety of words to describe the means to our results. Sometimes, it is a trick (space-saving trick, four-russians trick), other times, it is a technique (rounding technique, primal dual technique), or in some rare cases, an idea. It is difficult to see when a trick becomes a technique, and when an idea sparks it.

What are the top 10 ideas in theoretical computer science?

I have been asked this question during interviews (replace 10 by 5,3 whatever, and replace theoretical computer science by others if needed). There are a few courses in various colleges that are typically introductory: Anupam Gupta co-teaches a CMU course and there seems to be a much too general CS course at Harvard. But taking it up several notches, what are the top 10 ideas in theoretical computer course?