Currently there is no way of mapping the Product Category field in Zoho Books to Zoho CRM when using the Zoho Books Sync to CRM feature, which means CRM users are unable to filter, sort or access products by Category.  

Adding the Product Category to the Sync field list in the Books integration with CRM would allow users in CRM to manage products (view etc) much easier.  The field "Product Category" already exists in CRM, it's just not possible to sync the values using the current Zoho UI.