Light bulk indicates that the wholesaler has a very low minimum order quantity, usually below $500, and is willing to work with small businesses. This is in contrast to bulk wholesale which requires a minimum order of anywhere from $500 to $10,000 or more.
Light bulk is the optimal solution for eBay sellers or online retailers who are just getting started. The benefit of buying light bulk is that you are not risking a great deal if you buy wholesale items that do not make as much profit as you expect (though market research software can help to offset the risk). Furthermore, if you are short on storage space, you won't have the worry of having to store a lot of stock which can be overwhelming!