Sometimes, using a standard entity like product or invoice might not be the most optimal choice. Often due to the fact that there is quite a lot of business logic built into these entities. Therefore it is somtimes better to create you own entity instead. However, if you try to create a new entity with the name "Product" you will notice that it cannot be done since there already is an entity with that displayname.
The solution is quite simple, change the displayname of the built in product to "Old product" and remove all rights for all users to it and it will disapear for all normal users. You can then create your new entity with the displayname "Product".
Microsoft Dynamics CRM Architect