I've always called the overtones one can play on, say, guitar, harmonics, but some say the fundamental is also a harmonic. Which means my 1st harmonic is their 2nd harmonic. Confusing - to both of us, at least.
Why would the fundamental (usually an open string, but could be anywhere) ever be termed the 1st harmonic, since in my mind a harmonic is a note produced by splitting the fundamental into integral parts?
Partials is another term that is heard - but all harmonics are partials, and not all partials are harmonics...the plot thickens.