Formal:
* Etude: This is a common term for a short, technical piece used for practicing specific skills.
* Exercise: A general term for any short piece designed to improve technique.
* Study: This is another term for a piece that focuses on a particular musical concept or skill.
Informal:
* Warm-up: This term is often used for short pieces played at the beginning of a practice session to loosen up the fingers.
* Drill: A very focused exercise that emphasizes repetition of a particular technique or passage.
* Finger-buster: This is a more playful term for a piece that is particularly challenging to play.
* Workhorse: A piece that is frequently used for practice, often because it is helpful for developing a particular skill.
The best alternative will depend on the specific piece and the context in which you are using the term.