A biopic is a genre of film that tells the story of real people and their lives. The word "biopic" comes from the English "biographical picture." Essentially, it is a biographical film. The emphasis in the word "biopic" is on the "o" — biOpic.
Imagine a movie about some famous musician, for example, "Bohemian Rhapsody" about Freddie Mercury, or about a political figure, like "Lincoln" about the President of the USA. These are all biopics. They show us personal and sometimes unexpected moments from the lives of these people, as well as their journey to fame or important historical events.
So, if you see that a biopic is being announced in the cinema, know that you will be shown the story of a real person — with all their successes, failures, joys, and challenges.