What's an octave in music and how does it impact the overall sound of a musical composition?

An octave in music is a musical interval between two notes that have a frequency ratio of 2:1. This means that one note is double the frequency of the other. When two notes are an octave apart, they sound similar but one is higher or lower than the other. Octaves are important in music because they create a sense of harmony and fullness in a composition. They can add depth and richness to the sound, making the music more pleasing to the ear.