The word thrush has two completely unrelated meanings:

1. A small to medium-sized songbird known for its beautiful, melodious voice. Thrushes are found worldwide and include familiar birds like the American robin and the wood thrush. Many thrushes have speckled breasts and brown or gray feathers. In literature and poetry, the thrush often appears as a symbol of natural beauty and music: in The Secret Garden, Mary and Dickon hear thrushes singing in the garden as spring arrives. Some thrush species are famous for their ability to mimic other sounds they hear.
2. A fungal infection that appears as white patches in the mouth, most commonly affecting babies and young children. When someone has thrush, their mouth might feel sore or uncomfortable. Doctors can easily treat thrush with medicine.

The bird meaning is far more common in everyday conversation. When you hear someone mention a thrush in a story or see the word in a nature guide, they’re almost certainly talking about the songbird.