A unit or gathering of individuals united by a common interest or activity: A group of music students from school drove into the large city to attend a concert.

To gather or to place together people or items bearing similar characteristics: Mrs. Hastings grouped all the math students collectively in the library for intensive tutoring.

An alteration in behavior or physiology within a species brought about by signals that are directed in neither space nor time.

A simple example is social facilitation, in which an activity increases merely from the sight or sound (or other form of stimulation) coming from other individuals engaged in the same activity.

The hunting and retrieving of living prey by groups of cooperating animals.

A behavior pattern best developed in army ants.

The coordinated transport of a food item by two or more workers.

A cluster of about thirty galaxies that includes our own, the Milky Way.

Like other groups of galaxies, the Local Group is held together by the gravitational attraction among its members, and does not expand with the expanding universe.

Its two largest galaxies are the Milky Way and the Andromeda galaxy; most of the others are small and faint.

A group of minor planets that are clustered around two of the Lagrangian positions of the Jupiter-sun system; that is, a point in space at which a small body, under the gravitational influence of two large ones, will remain approximately at rest relative to them.

The first Trojan was Achilles, discovered in 1906.

These minor planets revolve around the sun in the Lagrangian points of Jupiter’s orbit and they are positions where a small body can be held, by gravitational forces, at one point of an equilateral triangle whose other points are occupied by Jupiter and the sun.

About forty Trojan planets are known; Achilles, the first, was discovered by Max Wolf in 1906. Of the named Trojans, Achilles, Hector, Nestor, Agamemnon, Odysseus, Ajax, Antilochus, Diomedes, and Menelaus are near the Lagrangian point 60° ahead of Jupiter. Patroclus, Priamus, Aeneas, Anchises, and Troilus are about 60° behind Jupiter.