It is the distance between two sounds. We can use this term to say: a tone interval, a semitone interval; actually, any distance between two notes is an interval. Generally this term is used with the definition of degrees, as we will see in following topics.
It is when there are different names for the same sound. For example, C sharp (C#) is the same as D flat (Db). Therefore, we can say that these notes are enharmonic.
Acute and Bass sounds
What makes a sound acute or bass is its frequency. High frequencies produce acute sounds while low frequencies produce bass sounds.
It is what defines if a sound is strong or weak. When we turn the volume button of a stereo we are alternating the intensity of the song. It is common to people say that when we turn up the volume, the sound is “higher”, but this definition is wrong because the volume does not change the frequency of the sound (it does not make it more acute or very bass). Volume only changes intensity.