"First purchase" refers to the first time someone buys or acquires something, typically referring to their initial transaction or buying experience with a particular product, service, or company. Full definition
The signup bonus of $ 300 (30,000 points) after first purchase makes this an easy choice as a card to apply for. (creditwalk.ca)
Only the cost of the very first purchase of shares is used. (retailinvestor.org)
Since your very first purchase with the credit card earns you 500 bonus points, you'll be well on your way to rewards that start at only 750 points. (creditcards.com)