As "Inc." or "inc.", it is an abbreviation for "incorporated", see corporation.

inc is in some MMORPGs a term used when a creature is incoming. (ie.: "inc a skeleton!")

Iglesia ni Cristo

Indian National Congress

International Concepts, a fashion label owned by Macy's Inc.

Iraqi National Congress

The (International) Noise Conspiracy (band)

International Network of Crackers, a major warez organization during the early 1990s.