Large corporation run as a single business, but made up of several firms (acquired through mergers or takeovers) supplying diverse goods and/or services. Berkshire Hathaway Inc. is one of the biggest conglomerates in the world, with ownership of insurance, utilities, financial, and retail companies. 
Read more

USAGE EXAMPLE

What started as a backyard business exploded into a huge conglomerate that employed hundreds of people spread over 3 states.