What does "shortening" mean? Is it different from "abbreviation"?

Solution 1:

In fact shortening is a kind of abbreviation.

According to MSN Dictionary There are four main kinds of abbreviations:

• Shortenings of words usually consist of the first few letters of the full form and are usually spelled with a final period when they are still regarded as abbreviations

cont. = continued

bus = omnibus

taxi = taxicab

zoo = zoological garden

bike = bicycle

• Contractions are abbreviated forms in which letters from the middle of the full form have been omitted.

Dr. = doctor

St. = saint or street

can't = cannot

didn't = did not

• Initialisms are made up of the initial letters of words and are pronounced as separate letters.

CIA (or C.I.A.)

NYC

pm (or p.m.)

U.S. (or US)

• Acronyms are initialisms that have become words in their own right, or similar words formed from parts of several words. They are pronounced as words rather than as a series of letters.

AIDS

laser

scuba

UNESCO

Please Visit this link to read more about abbreviation.

Solution 2:

Shortening also refers to fats used for baking. Probably not what you meant, though. :)

Solution 3:

I have been shortening the legs on my table, but I have not been abbreviating them!