An encounter group or similar group therapy method.

(mathematics) The group of 3×3 upper triangular matrices of the form 1ac\0 1b\0 0 1\ under the operation of matrix multiplication, arising in the description of one-dimensional quantum-mechanical systems.

(mathematics) Any of seven symmetry groups of infinitely long ornamented bands.

plural of frieze group

(group theory) The restricted wreath product mathbf Z₂≀ mathbf Z.

plural of lamplighter group

(mathematics) An abelian group constructed from a commutative monoid in a universal way.

(sports, jargon) A group in a multi-stage tournament which is unusually competitive, because the number of strong competitors in the group is greater than the number of qualifying places available for the next phase of the tournament.

(medicine) The basic system of categorizing blood by antigen type.

plural of blood group