According to the Code of Federal Regulations (14 CFR) Part 1,Title 14 defines a medical certificate as:
Acceptable evidence of physical fitness on a form prescribed by the Administrator
FAA Web Site
FlightPhysical.com endeavors to help aviators negotiate the aeromedical certification process. Legitimate goals of the program are to protect pilots, their passengers, fellow air travelers and the general public. Although few pilots relish the requirement, most in the aviation community understand its importance.
A person who meets FAA airmen medical standards, based on a medical examination and an evaluation of medical history, is entitled to a medical certificate without restriction or limitation other than those specifically stated. Individuals required to hold a medical certificate must have the actual certificate in their personal possession at all times when exercising the privileges for which they are licensed.
As you know (or will soon find out) flying is a fascinating and enjoyable experience, whether done for business or pleasure. Nevertheless, flying has the potential for serious consequences if not done properly and carefully. Just as it is unwise to fly an aircraft that is not airworthy, it is also foolish to fly as, or with, a pilot who is medically compromised.
Annual inspections are performed on all aircraft to assure they meet minimum safety standards. Routine medical exams accomplish the same goal for us human pilots. When an aircraft successfully completes an annual inspection, the A & P mechanic endorses the logbook indicating that the aircraft is airworthy. Similarly, when a pilot successfully passes the flight physical, the physician endorses the medical certificate which the pilot then carries with him/her each time they fly. This is public evidence that the pilot has met the medical standards for aircraft operation.
There are different classes of medical certificates depending on whether you you are performing duties as a commercial, airline, private or student pilot.
Aviation Medical Examiners (AMEs) are physicians who are desingated by the FAA and thereby authorized to perform flight physicals and issue medical certificates if the applicant must meet the medical standards. Find an AME.