A compound is a molecule which is composed of more than one element.  Table salt, for example, is sodium chloride (NaCl), a compound composed of the elements sodium (Na) and chlorine (Cl) in a 1:1 ratio. Pure sodiun is a metal, and pure chlorine is a poisonous gas. When chemically combined, however, sodium and chlorine form an edible compound. This is a simple example of organized matter having emergent properties: A compound has characteristics different from those of its elements.
Chemical compounds can be fairly simple, such as water (H2O), which is just one oxygen atom and two hydrogen atoms. Many are moderately complex, like sugars, which consist of no more than a few dozen carbon, oxygen, and hydrogen atoms, e.g. C6H12O6. Some are relatively huge (still not visible to the naked eye), such as DNA, which can contain millions of atoms in one double helix crystal.
In general, compounds containing carbon are referred to as "organic compounds".
- A compound is a substance with a fixed ratio of elements which determines the composition, and a particular organization which determines chemical properties. New World Encyclopedia
- Reece, Jane B., and Neil A. Campbell. Campbell Biology / Jane B. Reece ... [et Al.].