The protostar stage is a key step in the birth of a star when dust and gas are still condensing. Before a star officially forms, it begins as a cloud of gas and dust inside a region called a stellar nursery. These nurseries are like star "cradles" found in galaxies, and inside them, gravity starts pulling the particles together.

As this cloud contracts under gravity, it heats up and forms a dense core known as a protostar. This is not yet a full star because nuclear fusion hasn’t started, but it’s getting close. The protostar continues to pull in material from its surroundings and grows in size and temperature. Eventually, when the core becomes hot and dense enough, hydrogen atoms begin to fuse into helium, releasing energy — and that’s when a true star is born.

The protostar stage can last for millions of years, and during this time, the object may appear bright in infrared light due to the heat from the collapsing matter. Protostars are often hidden in clouds of dust, making them hard to observe with regular telescopes.

Let’s clarify the other options:
- **Star of Adam** is a fictional or symbolic term with no role in real astrophysics.
- **Alpha Stage** and **Stellar Genesis** sound scientific but are not formally used stages in stellar evolution.
- **Protostar** is the correct scientific term for this specific early phase.

In summary, a **protostar** is the in-between phase when a star is forming but has not yet ignited nuclear fusion. It’s one of the most critical and fascinating steps in the journey from gas cloud to shining star.