# Why is the ring of algebraic integers denoted by $\mathcal O_K$?

Why/when was the curly-O notation chosen for the ring of integers of an algebraic number field $$K$$?

• the ring of integers can also be characterized as the maximal Order of the field $K$ Mar 21 at 2:21
• @J.W.Tanner why is it called order? I only know the analytic sense of the word (less than, greater than) and like the size of a group or subgroup generated by an element; this seems to fit neither
– D.R
Mar 21 at 17:20
• click on the word Order in my comment above to see the ring theory sense of the word Mar 21 at 18:16
• The term order comes from the biological classification system, which also includes other terms adopted by mathematicians: class, family, and genus (and species in combinatorics).
– KCd
Mar 22 at 2:04