Products and Product Rules
Products are like "artists" for Non-music units. You can tell M1 to separate units with the same Product. They can be used like this: Say you have several PSA's that are about fund-raising; you have a PSA for the Red Cross asking for donations, you have another for a Homeless shelter and another for a local church. You could create a Product named: Fund Raising and click it into the Product Field on the Cards for these announcements. Then you could tell M1 to not schedule Fund Raising announcements anywhere near any other Fund Raising announcements. Most non-music units/cards will not need a Product, indeed most M1 users don't use Products at all.
Products can become a bit of a bother when they are un-wanted. If you import library data from mp3 tags and if any of your jingles or voice tracks or station IDs or promos have something entered in the "Artist" field on the mp3 tag, whatever is there will be imported onto the Cards for those units as Products.
This will normally cause no harm, BUT unnecessary Products can cause some unwanted 'stops' during scheduling for Product Rules violations.