What is characterized by having a fixed volume, being virtually incompressible, and taking the shape of its container?

The characteristics described in the question align closely with the properties of a liquid. Liquids have a fixed volume that does not change regardless of the container they are in, which distinguishes them from gases that expand to fill their containers. Additionally, liquids are virtually incompressible, meaning they do not significantly decrease in volume under pressure, unlike gases that can be compressed easily. Another essential trait of liquids is that they adapt to the shape of their container, flowing to occupy the bottom portion while maintaining that fixed volume. This combination of properties clearly defines a liquid, making it the correct answer to the question.