The term 'English Horn Relatives' refers to two different types of woodwind instruments, oboes and cor anglais. Oboes are five-letter instruments that produce a distinctively reedy sound. They are typically made of wood and have a double reed mouthpiece. Cor anglais, also known as the English horn, is a larger version of the oboe with a deeper, more mellow tone. It is also made of wood and has a double reed mouthpiece. Both instruments are used in classical music, jazz, and other genres.