It is called a tube. But under a microscope, it is customary to understand a device that was actually invented in order to obtain enlarged images of various objects or creatures, for example. It is worth knowing that there are so-called optical microscopes, there are also electron microscopes, and there are also X-ray microscopes.
One of the components of a person's success in our time is receiving modern high-quality education, mastering the knowledge, skills and abilities necessary for life in society. A person today needs to study almost all his life, mastering everything new and new, acquiring the necessary professional qualities.