A chord is the combination of two or more notes played simultaneously. This is the definition of chord, but there are innumerous possible combinations of making notes, resulting in many chords. So, to make musicians’ lives easier, each chord receives a name. This is based in the fundamental notes we already know (C, D, E, F, G, A, B).
Learn more here: http://www.simplifyingtheory.com/definition-of-chord/