The word "erithacus" is a scientific term that refers to a genus of birds commonly known as "old world thrushes." These are a group of small to medium-sized birds that are often found in Europe, Asia, and Africa. They are known for their beautiful songs and are part of the family Muscicapidae.
"Erithacus" is mostly used in scientific discussions about birds. If you're interested in ornithology (the study of birds), it's a term you may encounter often.