Galaxy groups and clusters are the largest known gravitationally bound objects to have arisen thus far in the process of cosmic structure formation. They form the densest part of the large scale structure of the universe. In models for the gravitational formation of structure with cold dark matter, the smallest structures collapse first and eventually build the largest structures, clusters of galaxies. Clusters are then formed relatively recently between 10 billion years ago and now. Groups and clusters may contain from ten to thousands of galaxies. The clusters themselves are often associated with larger, non-gravitationally bound, groups called superclusters.

Groups of galaxies are the smallest aggregates of galaxies. They typically contain no more than 50 galaxies in a diameter of 1 to 2 megaparsecs (Mpc) (see 10²² m for distance comparisons). Their mass is approximately 10¹³solar masses. The spread of velocities for the individual galaxies is about 150 km/s. However, this definition should be used as a guide only, as larger and more massive galaxy systems are sometimes classified as galaxy groups.

Caroline Crawford (born c. 1949) is an American rhythm and blues and disco singer and actress, who recorded as Carolyn Crawford for Motown Records in the early 1960s, and for other labels later in her career.

In 1963, at the age of about 13, she won a talent contest held by Detroit radio station WCHB, the prize for which was a contract with Motown Records. She recorded three singles for the label, an unsuccessful first release of "Forget About Me" (Motown 1050) being followed by "My Smile Is Just a Frown (Turned Upside Down)" (Motown 1064), written by Smokey Robinson. The record reached # 39 on the Billboard rhythm and blues chart. She also sang backup vocals for some of the Motown artists. Her final record for Motown, "When Someone's Good To You" (Motown 1070), released in December 1964, failed to chart and her contract was not renewed, although the record later became a favorite among British soul fans.

A few years later, she joined a girl group, Hodges, James, Smith and Crawford, put together in 1972 by William "Mickey" Stevenson. She released two singles with them, "Nobody" and "Let's Pick Up The Pieces", before leaving the group (which went on to achieve some success as Hodges, James and Smith). She then joined the group Chapter 8, but left them in 1976 to start a solo career; she was replaced in the group by Anita Baker.