Professional certification, trade certification, or professional designation, is more generally referred to as certification or qualification, and is earned by a person to assure that he/she is qualified to perform a job or task.
There are two general types of professional certification: some are valid for lifetime, once the exam is passed. Others have to be recertified again after a certain period of time. Also, certifications can differ within a profession by the level or specific area of expertise they refer to. For example, in IT Industry there are different certifications available for Software Tester, Project Manager, and Developer. Similarly, the Joint Commission on Allied Health Personnel in Ophthalmology offers three certifications in the same profession, but with increasing complexity.
Certification does not refer to the state of legally being able to practice or work in a profession. That is licensure. Usually, licensure is administered by a governmental entity for public protection purposes and certification by a professional association.
The other most common type of certification in modern society is product certification. This refers to processes intended to determine if a product meets minimum standards, similar to quality assurance.