Customer
Also known as: Buyer
A customer is a visitor who decided to give you money for what you made.
Out of the ten people who stopped and looked, three of them handed you money and took a cup. Those three are customers.
Something changed their mind. Maybe the price was right. Maybe the sign was friendly. Maybe they were very, very thirsty.
It is worth knowing which one it was, because you would like it to happen again tomorrow.
Color this: draw one customer. Draw a speech bubble. What did they say right before they bought?
For the grown-up holding the crayon box:
Asking what changed the mind of a buyer is the whole of customer research, and it is the least intimidating version of it a person will ever meet.