What does it mean when a team "clinches" in baseball?

Which manager has led the Dodgers to World Series titles in 2020 and 2024? Which manager led the Texas Rangers to the 2023 title, his fourth championship? Which manager won three World Series with the San Francisco Giants? Which manager led the Houston Astros to the 2022 title at age 73? What is the "Fall Classic"? What is the name of the MLB championship series that determines the American League pennant winner? What is a "pennant" in baseball? Which player hit three home runs in a single World Series game in both 1926 and 1928?