No - an acronym is an abbrevation of initial letters which forms its own word. SCUBA and LASER are acronyms. LCD and WWE are not.
lb is not an abbreviation for "pound". It is used to represent a unit of weight and is a concatenation (or contraction) of "librum".
"I've" instead of "I have" is also a concatenation (or contraction), not an abbreviation.
Interestingly, Dictionary.com use the first half of your example for abbreviations...
"2) A shortened form of a word or phrase used chiefly in writing to represent the complete form, such as Mass. for Massachusetts or USMC for United States Marine Corps."
Whereas they say this about acronyms:
"A word formed from the initial letters of a name, such as WAC for Women's Army Corps, or by combining initial letters or parts of a series of words, such as radar for radio detecting and ranging."