Industrial Unionism (similar to anarcho-syndicalism) is a union organizing method where all workers in the same industry are organized into the same industrial union (regardless of skill or trade). Thus giving workers in one industry, or in all industries, more leverage in bargaining and in strike situations. Making "an injury to one an injury to all", or, to put it another way, "the longer the picket line the shorter the strike."
Unions like the Industrial Workers of the World organized industrially and sought to organize the working class into One Big Union which would struggle for improved working conditions and wages today, and organize in order to carry on production when capitalism is overthrown by a general strike.
Compare with Craft Unionism.