This page has various notes designed to flesh out other pages on this site for those who are keen to go further...
A chord is a group of notes.
A major chord is the "default" chord type, and so the "major" is often left out of the chord name. For example, a minor seventh chord will have "m7" as part of the chord name: Cm7, F#m7, etc. But with a major chord, there is usually no label. "A" and "A major" mean the same thing.
In this site, I usually describe major chords in full, so that it is clear in each case which chord type we are talking about.