A subsidiary is a child company that is part of a larger company. Large conglomerate businesses tend to have subsidiaries for adjacent or separate businesses that deviate from the main business to preserve the brand, or to keep teams intact to not disrupt the culture and processes that are already working. Amazon is a good example of having subsidiaries. Amazon.com is an e-commerce store, while Amazon Web Services is an IT service. AWS operates as a subsidiary to Amazon.com with its own organizational structure etc.
in other words
The companies underneath a larger parent company.