What is the definition of an abbreviation?

An abbreviation is defined as a shortened form of a word or phrase. This definition focuses on how abbreviations compress longer terms into shorter, more manageable forms for ease of communication. For instance, "MRSA" stands for Methicillin-Resistant Staphylococcus Aureus, showcasing how a lengthy medical term can be condensed into a more succinct abbreviation that still conveys the same meaning. This is particularly important in medical contexts where quick and clear communication is essential for effective patient care.

The other options describe different concepts that do not directly relate to the definition of an abbreviation. Medical instructions provide guidance for procedures or treatments, synonyms refer to different words with similar meanings, and diagnostic classifications categorize diseases or conditions based on specific criteria. These concepts may be relevant in the medical field but do not pertain to the concept of an abbreviation itself.