A histogram is a picture made of bars that shows how a set of numbers is spread. You first cut the numbers into ranges — bins, like 10–20, 20–30 — and each bar shows how many fell in that range. The bars usually touch, because the ranges sit next to each other on a number line. That is the small difference from an ordinary bar chart, which often compares separate groups (cats, dogs, birds) and leaves gaps. People also use histogram as a verb: to histogram the data is to draw this kind of picture. The English maths scholar Karl Pearson made the word in 1891. It probably comes from Greek histos, a mast (a tall post, like the bar), plus gramma, a drawn mark — though some people have said historical plus diagram; that is a later guess, not the stronger story. Though actually, in class the shape matters more than the origin: touching bars, one measured thing, cut into bins.