In a parliamentary system, a prime minister can lose power if their party loses its majority in the legislature. This can happen during general elections, where the ruling party fails to win enough seats to secure a majority, or through a vote of no confidence, where the parliament expresses a lack of support for the prime minister.
In many parliamentary systems, the prime minister is typically the leader of the party that holds the majority in the parliament. If that party loses its majority, the prime minister may either resign or be forced to call for new elections. Alternatively, if they can form a coalition with other parties to regain a majority, they may be able to retain power. However, if no coalition can be formed, or if another party emerges as the majority, the prime minister will likely lose their position.