An octet is a group consisting of eight (8) elements. It has several specific meanings:

• Octet (music), a musical ensemble consisting of eight instruments.
• Octet (computing), an obsolete term for a byte often used in networks and RFC request for Comment pages by the IETF Internet Engineering Task Force.
• Octet rule, a simple chemical theory that states that atoms tend to combine so they each have eight valence electrons.
• Another term for Contubernium, the smallest unit within a Roman legion, consisting of eight soldiers with two non-combatant "servants" (actually support troops) attached.
• Octet, as used by Buckminster Fuller, is a combination of the words Octahedron and Tetrahedron, the two Platonic solids that in Fuller's geometrical system filled all space, e.g., octet truss.
• In poetry, a stanza consisting of eight lines.
• Octet (Christensen), a ballet by Willam Christensen (1958)
• Octet (Martins), a ballet by Peter Martins (2003)