Theory

Scales are collections of pitch classes to play together. There's a plenty of such known and used Note combinations.

Five notes is enough to construct the most simple and pleasant sounding Pentatonic scales. The most common scales nowadays are Diatonic sets of 7 notes, organized in a special way. Every note in such a scale has it's own distinct role as a Scale degree.

Breaking the diatonic rule the modernism era has discovered all the strange Symmetrical scales that bring us more complex emotional effects.

Let's not focus only on Western music theory, especially when it comes to scales. Indian Raga school has a much wider scope on note collections to be played and improvised over.