What Are Chords?

The music dictionary defines a Chord as:

"The sounding together of three or more tones..."

Here we will define a Chord as the sound you get when two or more notes play at the same time, most often in order to create a harmony.

In music we have single notes, one after the other, creating a melody such as you might sing or whistle, and then we have multiple notes that play at the same time and "dress" things up creating a harmony that often accompanies the melody. These harmony notes can be created using Chords.

Notice that the dictionary defines a chord as the sounding of three or more tones. The reason for this is because when a chord consists of only 2 notes it is formally thought of as an "interval".
It is acceptable to think of a chord as two notes or more.