In European context - gravy denotes a special type of sauce made from meat juices, collected after roasting. This gravy is very flavourful and thickened with roux, flour or cornstarch.
However in Indian context - (gravy meaning)
Gravy refers to a semi liquid mixture of vegetables, spices, fat, water and some times nuts/cream/curd in which meat or vegetables are cooked and used as an accompaniment to moisten the rice or roti.
There are different types of gravy. Click the link for basic indian gravies - http://www.cuisineindia.in/2016/12/basic-indian-gravies.html?q=basic+indian+gravy
Basic indian gravies - Brown gravy, White gravy, Makhni gravy and Green gravy. For video of makhni gravy click this link - https://www.youtube.com/watch?v=5wOSe1WnSpA