A scale is a series of single notes progressing up or down. You can imagine it like a ladder or a staircase of notes! Scales are used to arrange and give context to pitches.
Scales normally span a single octave, which means that a C major scale would begin and end in C (C D E F G A B C). However, some musical cultures use different types of scales. For example, the pentatonic scale (which only has 5 notes) is important in Scottish and Chinese music.