Okay, so you know how some songs have different parts that make up the whole song? Like how "Twinkle Twinkle Little Star" has verses that repeat and make up the whole song?
Well, in the Christian church, there is a type of music called "hagiopolitan octoechos" that is used in their worship services. This music has eight different parts, or tones, that are used in different parts of the year.
Each tone has its own set of melodies and hymns that are sung during certain times of the week and throughout the year. For example, Tone One might be used during the first week of Lent, while Tone Four might be used during the third week of Advent.
This music is very important in the Christian church because it helps people worship and connect with their faith. It has been used for many centuries and is still used today in traditional Christian services.