An Order is an Amazon transaction between you and a customer.
A SKU is the unique number you assign when listing an item with Amazon. SKUs are unique to your Seller profile and allow you to track performance for your individual items. SKUs are unrelated to a product’s ASIN, which is assigned by Amazon.
Marketplace refers to an individual country’s Amazon marketplace, such as the US or FR.
Market refers to an aggregated view of all marketplaces, such as the EU or NA markets.