Opus is a Latin word for work. The plural of opus is opera. It is used in many fields, notably in architecture and in music.

• In music, pieces of some composers' music are given opus numbers which generally run either in order of composition or in order of publication.
• In architecture, it specifically describes a technique or a method or a style of connecting building elements, following the studies on Roman architecture. Roman building styles are commonly classified as:
  • Opus incertum
  • Opus testaceum (also called Opus latericium )
  • Opus caementicium
  • Opus reticulatum (also called Opus certum )
  • Opus siliceum
  • Opus quadratum
  • Opus vittatum
  • Opus mixtum
  • Opus spicatum
  • Opus alexandrinum
• Opus Dei (God's work) is a conservative Roman Catholic organization founded in 1928.
• Opus the penguin is a character in various comic strips by Berkeley Breathed.
• Opus is a comic strip by Berkeley Breathed.
• Directory Opus is a file manager originally for the Amiga computer and now for Windows.
• A "magnum opus" (or "opus magnum") is a great work or, more commonly, the greatest work of a person. Magnum is Latin for great.