I've often been asked about the differences between an herb, a spice and seasoning. The answer is in two parts.

1. The first part of the answer addresses the difference between an herb and a spice. An herb is the leaf or petal of a plant or flower that is either dried or used fresh. There are a variety of herbs, such as St. Johns Wort, which are used for medicinal purposes, and herbacious plants used for decorating a room. However, for our purposes here, we will concentrate on the culinary herbs like basil, oregano, thyme, etc. Spices, on the other hand, are various parts of the plant, other than the leaf or petal, that are typically dried. Some examples of spices include cinnamon (the dried bark of small evergreen trees), peppercorns (the fruit of the flowering vine of a pepper plant in the botanical family Piperaceae), and saffron (the dried stigma of the crocous flower; also known to be the most expensive spice in the world due to the way it is harvested).
2. The second part of the answer addresses the ingredient's relationship to the flavor. Herbs and spices add flavor to the dish, where as seasonings bring out or enhances the flavor of the dish. A good example of seasoning is salt. Yes salt adds salty taste to the dish but its main characteristic is that it brings out the flavor of the food that it is added to.

Is this really important? Probably not. What is important is knowing what each herb, spice, and seasoning does to the flavor of the food. There are herbs that usually go well with certain types of meats, and there are spices that are inherent of each cuisine. For example, thyme goes well with poultry, and just about any other meat product it is added to, whereas if you were cooking an Asian dish, chances are that you probably will not use rosemary. Tumeric is typically found in Indian dishes as part of a curry mix, whereas violets are typically found in French provencial cooking. Of course, these are only rules and rules are made to be broken. Overall, the best indicator of which herb, spice, or seasoning goes well for each dish is your taste.