No such thing as a silly question 😃
It’s a product you pitch or refer customers to, and if they buy it, you receive a commission per sale. For example, with Amazon Affiliates, you can include an “affiliate link” in say your Medium article, referring readers to say a book you recommend. If they buy the book you get a small commission/cut from Amazon.
A lot of people make serious money from through affiliate marketing.
Hope that makes sense…