Schläfli double six

Etymology
Named after Ludwig Schläfli.

Noun

 * 1)  A configuration of 30 points and 12 lines. The lines can be partitioned into two subsets of six: each line is disjoint from (skew with) the lines in its own subset of six lines, and intersects all but one of the lines in the other subset of six lines. Each of the 12 lines of the configuration contains five intersection points, and each of these 30 intersection points belongs to exactly two lines, one from each subset.