A noun derived from the prefix "octo-," meaning eight, and influenced by the word "duet," the word "octet" can mean any grouping of eight objects that are similar and used together as a set. However, it often specifically refers to such groupings in relation to music, literature, chemistry and computers.
An octet in musical terms often refers to eight singers or musicians who perform together in a complementary fashion. Similarly, octet is also defined as a piece of music specifically written to be performed by eight singers or musicians.
In poetry, an octet is another word for octave, which stands for eight consecutive and cohesive lines forming a stanza in a poem, or a poem consisting of only eight lines. Often, octet specifically refers to the first eight of the 14 lines comprising a Petrarchan sonnet.
In chemistry, when atoms combine to form molecules, they lose, gain or share electrons. The octet rule refers to the tendency of atoms to combine with other atoms in such a way that each atom possesses or shares eight electrons in its valence shell. Each atom's set of electrons form an octet, a stable shell of eight.
In computer terminology, an octet means an eight-bit byte or a storage unit consisting of eight bits. The term was invented to prevent confusion in the computer world over conflicting definitions of the word "byte."