What is?

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“What is?” is a selection of articles which explain an aspect of Math and/or Computer Science. The idea for “What is?” is taken from the immensely helpful list by Professor Nicholas J. Higham which was itself inspired by a similar series from the AMS.

My collection will deviate slightly from Prof. Higham’s list. I will try to explain each concept at three levels (where reasonable and I have time):

1. General - An acturate but not precise analogy understandable by a general reader.
2. Some Training - An acturate but not precise analogy but with precision higer then that of the general level.
3. Mature - An acturate and precise (or nearly so) description of the concept.