What is Abbreviations and Acronyms:

An abbreviation (from Latin brevis, meaning short) is a shortened form of a word or phrase.

Usually, but not always it consists of a letter or group of letters taken from the word or phrase. For example, the word abbreviation can itself be represented by the abbreviation abbr, Abbrv. Or abbrev. Abbreviations should not be confused with Contractions or Acronyms (including initialisms), with which they share some semantic and phonetic functions, though all three are commonly connoted by the term “abbreviation.”

• An abbreviation is a shortening by any method (e.g. Prof; St; B.Tech; B.A. Mon ;)
• A contraction is a reduction of size by the drawing together of the parts . A contraction of a word is made by omitting certain letters or syllables and/ or bringing together the first and last letters or elements. (e.g: Dr. bk; can’t; they’re)
• An acronym is a word formed with te first letters of the words in the phrase. (e.g; UNESCO; AIDS; SIM (card) ; radar)
• An abbreviation may be made either by omitting certain portions from the interior or by cutting of a part; a contraction is an abbreviation, but an abbreviation is not necessarily a contraction.

More examples:
Abbreviations:

PA – Personal Assistant
PS – Personal Secretary/ post Script
BPO - Business process outsourcing
KPO - knowledge Process outsourcing
B. Tech. – Bachelor of technology
SBI - state bank of India
RRB - Railway Recruitment Board

Acronyms:

TAFE – Tractor and Farm Equipment
TANSI - Tamil Nadu Small Scale Industries
RAM - Random Access Memory
ROM - Read Only Memory
VISCOM - Visual Communication
AIR – All India Radio