Often when people are convicted of a shoplifting offense they want to know exactly what is shoplifting. How is it different from any other theft offense.

One way to answer this question, is to look at the theft laws for one state. In particular we'll look at South Carolina theft laws. 

Shoplifting Can Be Just Moving An Item in a Store

Some people think shoplifting means taking an item out of a store. This doesn't have to be the case. Simply moving an item in a store without the owner's permission can be shoplifting: Here's part of the law:

"...takes possession of, carries away, transfers from one person to another or from one area of a store or other retail mercantile establishment to another area, or causes to be carried away or transferred any merchandise displayed, held, stored, or offered for sale by any store or other retail mercantile establishment with the intention of depriving the merchant of the possession, use, or benefit of the merchandise without paying the full retail value;"

This means that if you take something from the clothing section and put it in the hardware section, this is shoplifting. The presumption is that you might be trying to move something so that you can take it later. But even if you aren't doing this, it's still theft.

Another thing that people do is move items from one area (the full price area) to another area (the sale area). This is also shoplifting:

"...transfers any merchandise displayed, held, stored, or offered for sale by any store or other retail mercantile establishment from the container in which it is displayed to any other container with intent to deprive the merchant of the full retail value."

Modifying a Price Tag is Shoplifting

If you in any way modify a price tag, this is also shoplifting. Maybe you peel off a tag or put a tag from another cheaper item on the existing tag so you can pay less for it. It's still shoplifting. Again, here's the law:

"...alters, transfers, or removes any label, price tag marking, indicia of value, or any other markings which aid in determining value affixed to any merchandise displayed, held, stored, or offered for sale in a store or other retail mercantile establishment and attempts to purchase the merchandise personally or in consort with another at less than the full retail value with the intention of depriving the merchant of the full retail value of the merchandise;"

So shoplifting is really any time a person makes an item unavailable for a merchant to sell at they price they indend to sell the item. This means that making the price lower, modifying the item or indeed taking the item are all forms of theft.