A lookup is also known as a 'keystroke' or 'keypress', which is the press of a button on your keyboard. When a user types in an address on the search field, they will be inputting multiple keystrokes. This auto-populates the closest address suggestions via a displayed drop down. Once a user selects a full address from the suggestions drop down, they have a verified address.
At AddressZen, we only charge per verified address. You can view our pricing here. Our plans include unlimited keystrokes, which allows a user to input data in an address field at no cost.
Read our guide about verified addresses to further understand purchasing credits.