1. A Mass for the repose of the soul of a deceased person. This is the most common and traditional meaning of the word, referring to a religious service in the Catholic Church, often featuring solemn music.
2. A musical composition, especially a choral work, commemorating the dead. This is a more general meaning, encompassing any type of music written in remembrance of someone who has passed away.
3. More broadly, anything that expresses sorrow or mourning. This can include poetry, literature, or even a specific place or object associated with grief.
In essence, a requiem is a way of remembering and honoring the deceased, often with a focus on peace and solace.