收到国外客户的名片，在地址栏边上有些会有NIP后面带上一串数字

(Polish: NIP)The Tax Identification Number
Registration of tax-payers – the tax identification number (Polish: NIP)
Natural persons, corporate bodies, and organisational units which do not have any legal status and which are qualified as tax-payers by other acts have to be listed as tax-payers. This is defined by the Act from 13 October 1995. They are given tax identification numbers (NIP). The NIP is also given to legal subjects which, on the basis of other acts, pay the social security or medical insurance.
In order to be given the NIP, it is necessary to apply for it in the tax office (appropriate for one’s place of residence). Every tax-payer can be given only one NIP no matter the number of taxes and the types of taxes he or she pays, and the number and types of businesses and companies he or she runs.