Here's a small glossary of terms you might here when discussing organic gardening.
Organic matter is anything that was once alive.
This encompasses a range of objects from a dead bacterium to a dead whale, from fallen leaves to gasoline. For your garden you'll be mostly concerned with having organic matter in your soil including dead leaves, grass, roots and microorganisms and bird, insect, cow, horse and frog poop. You'll need to have your soil tested by an expert if you want to determine soil organic matter, but if your plants are healthy, don't worry about it. Mulch is a layer of material placed over the soil to hold in water and discourage weeds while allowing nutrients and air to enter the soil. Most commonly it is an organic material that takes a while to decompose.