Tracking number or tracking code is a unique number assigned to each package, which allows you to monitor the movement of the parcel between the countries or even inside one country.
Tracking numbers can be international or traceable only within the country of the sender.
The tracking number in the format of the Universal Postal Union looks like RA123456789CN, where the first 2 letters are the type of package and the last 2 letters are the code of the country of origin. Packages with such numbers can be tracked right until delivery.
Other shipments can be delivered by courier, transport and logistics companies, and how tracking codes look can vary a lot: CTAFT0000160477YQ, UPAAB000000251682107, AEL10105033654UA, SGADN143797855. Such packages are not always trackable in the recipient's country, and you'll have to wait for notification from the Post Office or a call from a courier company.