The letter O is used for a number of different purposes in mathematics. The double-struck is sometimes used to represent octonions. The symbols (sometimes called the O-symbol, O-notation, or "big-O") and (sometimes called "little-o") are a type of asymptotic notation collectively known as Landau symbols.
O
See also
Landau Symbols, OctonionExplore with Wolfram|Alpha
References
de Bruijn, N. G. Asymptotic Methods in Analysis. New York: Dover, pp. 3-10, 1981.Referenced on Wolfram|Alpha
OCite this as:
Weisstein, Eric W. "O." From MathWorld--A Wolfram Web Resource. https://mathworld.wolfram.com/O.html