In very simple language, when we play several notes together at the same time, we call the sound created as a chord. For example, right now, just place the number 2 finger of your left hand (the longest finger) on the second fret of the fourth string of your guitar, you don't need to hold any frets and play the four lower strings at the same time.
Well, if your guitar is in tune, you will now have the sound of a type of E minor chord or Em. Pay attention! You cannot put your finger anywhere and say that you are playing a chord. When playing several notes at the same time, we call them chords so that special and meaningful notes are played together
Chord, which is called Chord in English, is a French word (Accord) which, of course, is pronounced by the French. A chord is several sounds that are heard together at the same time. If we play the notes of the chord with intervals and in succession, it is called Arpège. Cognition of Chords is the science of knowing the types of chords, how to make them, and naming them.