What is a thumbnail sketch, and what is its purpose?

Thumbnail sketches are often sketches done by an artist. They are quick and fast with no fixes or changes involved in it. A thumbnail sketch is used to get the basic concept or idea of the sketch. For example, if the artist feels like creating a drawing, the artist very well might create a few thumbnail sketches to get more of an idea that they want to draw. They also may do a thumbnail sketch to see how they want objects in their piece to line up.            

this gave me 100% on ed2020, so I hope it is useful to others.

the answer is counterpoint.

counterpoint definition: "the art or technique of playing a melody or melodies in conjunction with another, according to fixed rules."

counterpoint is present in a lot of baroque music- such as bach (notably his wtc prelude and fugues) and scarlatti, but can also be found in music by mozart, beethoven. it can even be found in music as modern as john williams!