This definition appears very rarely
Samples in periodicals archive:
The Tribeca of the title comes from Triangle Below Canal Street, the geographic setting for these hourlong explorations of postmodern Manhattan.
Tribeca is an acronym for Triangle Below Canal Street and has most recently been jumpstarted by Oscar-winning actor Robert De Niro who invests heavily in numerous properties throughout the area and opened several businesses including the world-famous Tribeca Grill.
TriBeCa, technically part of Soho, is the triangle below Canal Street with the Hudson River to the west, Chambers Street to the south and Lafayette Street to the east, although some Tribecans say Broadway is the eastern boundary.