Enameled copper is a copper wire that is sometimes then silver plated, then coated with a colored enamel (or sometimes clear).  It offers an affordable alternative to sterling or gold, and a huge range of gorgeous colors.  Also, because the metal is coated, it offers some degree of hypoallergenicity for people with metal sensitivities.  Also, it will not tarnish (although sometimes the lighter colors and particularly silver may yellow over time, and there is no way to polish it back up).

 I use "EC" for maille and also for wire wrapping, and it is one of my favorite choices. Because it is not solid metal through and through, it's not as strong as other metals, so if you are rough on your bracelets or necklaces, I don't recommend it as the structure that gives support to the piece.  But for economy and color, it's unbeatable.