Sorrow was a feeling of deep sadness or grief that could be caused by a number of events, such as: the loss of a loved one, a disappointment, a failure, sympathy for another's suffering, and an injury done.
In 2293, General Chang quoted Romeo and Juliet's line "parting is such sweet sorrow" when departing after dinner aboard the USS Enterprise-A. (Star Trek VI: The Undiscovered Country)