If your mother becomes rhapsodic describing a delicious meal, she is so delighted with her food that she's practically composing poems in praise of the butternut squash soup.
The straightforward meaning of the adjective rhapsodic is "like a rhapsody," but in usage it borrows chiefly from a figurative use of rhapsody, "effusively rapturous or emotional expression." You might come across the phrase "to wax rhapsodic," which is pretty much the same thing as "to gush." People who are in love, for example, tend to wax rhapsodic about the objects of their affection.