These cards get described in many ways especially on ebay, this page will break down and explain the basic terms used.
Below is a very common callout that you could find on packaging, in an ebay listing or on a stores web site. The owners manual for your device may not list all these terms.
Kingston 16GB SD HC Class 4
Kingston is the manufacturer of the card. This is one that may not be in your owners manual. There are many very good manufacturers of these cards, the main thing to look for is the warrantee offered.
16GB is the amount of memory the card has or Capacity. I have another article that explains how much a gig will hold at http://www.bukisa.com/articles/445705_how-much-will-a-sd-card-hold-
SD describes the physical size of the card. There are three sizes SD, MiniSD and Micro SD. There are adapters on the market that will allow you to use smaller cards in larger slots as follows.
HC is a capacity rating for the card. There three ratings SC,HC and XC. These are not interchangeable. The SC rating may not appear on the card or in the listing it is the default.
Class 4 describes the speed class of the card. This may or not be in the description and there are many ratings. This is an area that can get you in trouble as all these cards may not work in your device.
There are two relatively new speed classes on the market with a different bus. These are UHS-I and UHS-II. Unless your device is specifically rated for these cards your device will not be able to read them.