Yes. An item is a piece of equipment to which you assign a name (e.g., microphone stand), a price, internal and external comments, etc. Each item has its own QR code.
An item can consist of multiple serial numbers. These are single pieces of the item, and each serial number has its own unique QR code.
For expensive equipment items, it's useful to add QR codes to each of their serial numbers. Bulk equipment such as cables don't need QR codes for each serial number; you could add one QR code to the item instead.
For example: If you are booking out 4 microphone stands for a gig, you are not interested in which ones specifically are going out. So these stands will all have the same QR code label.
If you are renting a Pioneer CDJ2000, you might want to select a specific one and keep track of its usage. So you will assign a specific serial number to each CDJ2000, and each serial number will have its own unique QR code.