They are commonly known as acronyms. Some examples are..
LASER (Light Amplification by Stimulated Emission of Radiation)
POSH (Port Out Starboard Home)
AIDS (Acquired Immune Deficiency Syndrome)
RADAR (RAdio Detection And Ranging)
ROTFL is the initial letters of the words ofRollingOnTheFloorLaughing
An acronym is a series of letters that stand for something (each letter stands for a word). For example, SCUBA (Self Contained Underwater Breathing Apparatus) PFD (Personal Floatation Device) MAD (Mutually Assured Destruction)
The letters inside the ichthys, "ΙΧΘΥΣ", stand for "Jesus Christ, Son of God, Savior" in Greek.
an acronym
An acronym is an abbreviation formed by combining the initial letters in words or part of a series of words
Stand, for one.
Equal Employment Opportunity Commission
An acronym is a word made up of the initial letters of a name or phrase. E.g. The acronym NASA stands for National Aeronautics and Space Administration
An acronymis an abbreviation formed from the initial components in a phrase or a word. These components may be individual letters (as in CEO)
a word formed from the initial letters of other words (e.g., radar, laser).
characters can sometimes stand for letters, but hieroglyphs stand for whole words.
acronym stads for A word formed from the initial letters of other words (e.g., radar, laser).