A sauce made in the pan from the browned, coagulated juices left after meat is roasted or pan-fried. It is made by deglazing, that is by adding liquid to the pan and scraping and stirring the flavoursome bits into it as it boils. The liquid used may be vegetable cooking water, stock, wine, cream or a mixture of these.
A good gravy should be well flavoured and light-bodied so that it ‘shows the meat’. It is usually rather scant since the rich meat flavours are lost if too much liquid is added. A thin or clear gravy (in French, jus), achieves its body by reduction and perhaps a little butter swirled in at the end.
Purists frown on the use of flour to thicken a gravy, but since a great many people like gravy made this way, and since it is, after all, simply a roux‑based sauce like many respected classics, it seems unreasonable to decry it. The points to watch are that the flour is browned slowly to give good flavour and colour and that you use just enough to give body, without making the gravy heavy and blanketing.
For a gravy which is lightly thickened but still clear, make jus lié by thickening clear gravy with a little arrowroot, or add body with two or three spoonfuls of vegetable purée.