A number of stars moving in the same direction with the same speed.

1. A family of elements with similar chemical properties.

2. A combination of bonded atoms that behave as a unit under certain conditions, for example, the sulfate group, SO₄^2-.

A subdivision containing a number of voice channels, either within a supergroup or separately, normally comprised of up to 12 voice channels occupying the frequency band 60-108 kilohertz; each voice channel may be multiplexed for teletypewriter operation, if required; the number of voice channels which may be simultaneously multiplexed for teletypewriter operation will vary according to equipment design.

A lithostratigraphic material unit comprising several formations.

A set G with an associative binary operation where g₁.g₂ always exists and is an element of G; each g has an inverse element g^-1, and G contains an identity element.