There are seven notes of music and two different systems of musical notation.
The origin of the syllabic notation is due to the Italian monk Guido d'Arezzo (XIth century) who used the first syllables of a Latin hymn to name the music notes:
DO (or UT) - RE - MI - FA - SOL - LA - SI
Mainly used in Anglo Saxon countries (and so in jazz), it uses the letters of the alphabet:
A - B- C- D- E- F- G
The German music notation uses a H and not a B (SI in alphabetical notation):
A - H- C- D- E- F- G
Syllabic musical notation is used by Italian, Portuguese, Greek, French, Russian, Flemish, Romanian, Spanish, Hebrew and Turkish people.
Alphabetical musical notation is used by Anglophone countries.
German Alphabetical notation is used in Germany, Poland, Russia, Scandinavia.