A note is a single musical sound.  You can speak of "a group of notes" being played without needing to know exactly what those notes are.

However, once you try to describe which notes they are, it is important to be clear about a few basic terms.

Note Names

Often in music, you will be referring to the notes by their names.  The note names in music are based on the letters A, B, C, D, E, F and G, with perhaps a sharp (#) or flat (b) symbol appearing after the note letter.

Notes fall naturally into groups of twelve, known as octaves, and notes exactly one octave apart are given the same note name, because they sound the same as each other, only lower or higher.

Sometimes, the same note can have more than one name.  For example, the note C# is the same as the note Db.  If the note is part of a chord or scale, there are rules for which name is more appropriate.

Note Pitches

Even more precise than knowing the name of a note is to know also which octave it belongs to.

This specifies the exact pitch of the note, or how low or high it sounds within our audible hearing range.  Usually pitch is indicated with an octave number after the note name, such as C#4 instead of just C#.

Within an octave, notes are arranged from C to B, and not, as you might expect, from A to G.  So the following pitches are in increasing order: ...  , B3, C4, C#4, ...  , Bb4, B4, C5, ...

Degrees

The term degree is used for a component note of a chord type or scale type.  The essential property of a degree is its interval from the root note.

Degree names, with possibly a sharp (#) or flat (b) symbol before the number, range from 1 to 13 with chord types, and from 1 to 7 with scale types.

Only some of the possible degree names are commonly used.  For examples, see the standard chord types and scale types.