Explanation:

Product Items are records that track the location, quantity, and status of a product in inventory[43]. Product Items can be used to better understand the distribution of a critical and expensive part across all inventory locations as the part is reused and restocked. Maintenance Plan is a feature that defines the recurring service schedule for an asset or a product[44]. Entitlement Plan is a feature that defines the terms of support for customers such as number of cases allowed or response time[45]. Assets are records that represent products that customers have purchased and that require service[46].

References: https://help.salesforce.com/s/articleView?id=sf.fs_product_items.htm&type=5

https://help.salesforce.com/s/articleView?id=sf.fs_maintenance_plans_overview.htm&type= 5

https://help.salesforce.com/s/articleView?id=sf.entitlements_templates_overview.htm&type =5

https://help.salesforce.com/s/articleView?id=sf.fs_assets.htm&type=5