A more thorough explanation:

Definition: A fetus is a developing mammal that has not yet been born, especially in the later stages of development. It is also spelled as foetus. It is different from an embryo and a zygote.

• A pregnant woman can feel the movements of the fetus in her womb.
• The ultrasound showed that the fetus was healthy and growing properly.
• The fetus is fully formed by the end of the second trimester.

The examples illustrate that a fetus is a developing mammal that is still inside the mother's womb. It is in the later stages of development and has already formed its major organs and body parts. The examples also show that doctors can monitor the health and growth of the fetus through ultrasound and other medical tests.