A holding company is a company that owns part, all, or a majority of other companies' outstanding stock. It usually refers to a company which does not ...
en.wikipedia.org/wiki/Holding_company

IHC is a holding company with more than $1 billion in assets that is principally engaged in the life and health insurance business and the acquisition of ...
www.independenceholding.com

definition of holding company - A company that owns enough voting stock in another firm to control management and operations by ...
www.investorwords.com/2327/holding_company.html

one of the meanings of "agrupar" being "to assemble", I wonder if the term could refer to companies which assemble goods using components made by manufacturing companies. It depends on the rest of your context obviously.

Part of what is termed packaging in English is sometimes described as agrupación. See references below:

Incidentally, I have my doubts about 'holding company' because this is a list of company activities and not types of ownership.