Product Availability refers to the availability or sale of a product in one or more of your Locations.
Let's take for example:
Your company has 2 Locations - Location 1 and Location 2
Product you want to sell - Pasta Carbonara
you want to sell this product only in Location 1
When configuring or editing the product at the Availability menu point you need to select Location 1. This way the product will appear in the POS of Location 1.