Kind codes are part of the patent number and are affixed at the end of the number. The kind code includes a letter, and may also include a number.  It indicates the status and/or type of patent. Sometimes it may also be called as "status codes"

Examples: US7293573B2, or US20050117326A1. 

"A" indicates patent application, “1” indicates initial publication of applications while "B" indicates granted patent,  "2" indicates this granted patent having a previously published pre-grant publication. 

Commonly used kind codes:

National authorities use various kind codes depending on their publication policies. See detailed kind codes explanations by USPTO, EPO, and WIPO.

Strategic applications:

• A quick, at a glance way to identify the status of a patent (is it an application or has it been granted? Is it a translation?) or the type of patent (is it a utility patent or a plant patent)?