Definition of an acquisition in online advertising
When you are acquiring something, you are getting hold of something new or gain ownership of something new.
In online advertising the term acquisition may be used to describe the act of getting new customers.
Acquisitions could easily be confused with actions, since both are part of the term CPA. But while actions in Cost Per Action means a wide range of actions (a purchase, a form submission etc.), the acquisitions in Cost Per Acquisition usually means that the advertiser gets a new client/customer in its portfolio.
Both acquisitions (CPA), actions (also CPA), leads (CPL) and orders (CPO) are often used for the same purposes, and the naming depends on the specific systems and the advertising models (for example affiliate marketing).