The March birth flower – the daffodil is the official common name for all of the plants that fall into the genus Narcissus. Most people use the term “daffodil” when referring to the large familiar bulb, trumpet-shaped flowers that bloom in yellow and/or white each spring.

A house with daffodils in it is a house lit up, 
whether or no the sun be shining outside.  ~ A.A. Milne

Is it a daffodil or a jonquil?

The term jonquil actually refers to a specific type of daffodil known as Narcissus jonquilla. In some parts of the country jounqil is the name that is often used as a more general term for daffodils.The jonquilla variety is most easily identified by their dark green, tube-shaped leaves as compared to other types of daffodils which have flat leaves. Jonquils also tend to have clusters of several flowers rather than just one bloom.

daffodils, That come before the swallow dares, and take The winds of March with beauty.         ~William Shakespeare

More info:  American Daffodil Society – http://daffodilusa.org
General guidelines and sources for growing and caring for your daffodils.