Blighty is an old-fashioned and affectionate term for Britain as one's home country, especially when abroad or after having come back from abroad. Much used in sentimental songs and exclamations like "Oh to be back in Blighty".
It's Arabic in origin, via Hindi. The Arabic wilayat meaning 'province' gave rise to the Hindi bilayati meaning 'foreign'. This was applied to things European and specifically British, from which it passed into English military slang as Blighty.
In the First World War a Blighty wound, or a Blighty one, or just a Blighty, was one just serious enough to get you sent back home but not enough to wish you hadn't got out of the war this way.