Member of the woodwind family. A double reed instrument. Is NOT a "big oboe". Pitched a fifth below the oboe, in F. In orchestral works, is usually used to convey "sad" emotions. Has a deeper, more mellow sound due to the rounded bell. Is not English, despite the name. It's actually French. This is from a mis-translation of its other name, "cor anglais", which means "angled horn" but can also mean "English horn".
That English horn solo made me cry.