There are times when you want a product that users can sign up for / buy, but you don't want it to show up as an available product for ALL users.  This is where "Invisible" products should be used.

Create or Edit Product

Create a new Product, OR Edit an existing product.  Set the status to Invisible.  You can use any product type with this, but make sure you have sign up options to something.  (otherwise there would be no point in having this product at all)

Share Product

Once your product is all done and set to invisible, you'll want to grab the "Teaser Link" so you can privately invite people.  To get that, simply click on "Products" and click on the Gear Icon next to the invisible product.

Anyone who goes to the Teaser Link will be able to see and sign up / buy the product.