Opera buffa (literally, "comic opera") is a type of opera that is light-hearted and often humorous in nature. It typically deals with everyday situations and characters, and often has a happy ending. The music in opera buffa is often lively and upbeat, with plenty of comic moments and arias. Some famous examples of opera buffa include The Barber of Seville by Gioachino Rossini and The Marriage of Figaro by Wolfgang Amadeus Mozart.
Opera seria (literally, "serious opera") is a type of opera that is more serious in nature and often deals with historical or mythological subjects. The music in opera seria is typically more complex and dramatic, and often features elaborate arias and ensembles. Some famous examples of opera seria include Handel's Julius Caesar and Mozart's Don Giovanni.
In summary, opera buffa and opera seria are two different sub-genres of opera that differ in their subject matter, musical style, and overall tone.