Initialism of One Country, Two Systems, the political structure by which Hong Kong and Macau are administered separately from mainland China. Chinese: 一國兩制／一国两制 (yī guó liǎng zhì).

Alternative spelling of Oct.

(computing, informal) Abbreviation of octal.

(medicine) Initialism of optical coherence tomography: an optical signal acquisition and processing method that captures high-resolution three-dimensional images from biological tissues.

Abbreviation of October.

Form of octa- or octo- used before a vowel.