Transnational organized crime
The Thomson Corporation, by ticker symbol on the New York and Toronto Stock Exchanges
Tactical operations center, a command post for police, paramilitary, or military operations
Taste of Chaos, a winter/spring concert series
Tournament of Champions (debate), a prestigious national high school debate tournament
Train operating company in the UK
The Objectivist Centre, part of The Atlas Society
Third Order of Our Lady of Mount Carmel, also known as the Lay Carmelites.

Places

Science and technology

Table of Contents, in optical disc authoring
TOC protocol, an instant message communications protocol
Translocon at the Outer membrane of Chloroplast, in Beta barrel
Troponin C, part of the troponin complex in biochemistry
Theory of computation, a branch of computer science
Total organic carbon, used as a non-specific indicator of water quality or the amount of organic carbon in a geological formation, particularly the source rock for an oil play.
TOC1 (gene), a gene that regulates circadian rhythm in plants

Theory of Constraints, an overall management philosophy
Top of climb, an aviation term
Teacher On Call, the same as a substitute teacher
"T", in the World War I Western Front "signalese" and the RAF phonetic alphabet
Theory of change, a methodology for planning, participation, and evaluation that is used in the philanthropy, not-for-profit and government sectors to promote social change. Theory of Change defines long-term goals and then maps backward to identify necessary preconditions.