Acquisition
One company buying control of another company or of specific assets.
An acquisition transfers control. A share acquisition buys the company itself, taking its liabilities along with its assets. An asset acquisition buys specific things, which is how individual brands change hands without the seller's other businesses moving.
When a single brand moves between companies without the whole business following, it is nearly always an asset deal. Ferrero buying Butterfinger and Baby Ruth from Nestlé in 2018 is one: Nestlé kept its confectionery business everywhere outside the United States.