Jus is produced after cooking meat, by removing the fat from the resultant liquid or residue and after adding water bring to the boil and reduce.
Beef, veal, chicken and land meats can all produce the base of a good jus.
Other styles of jus can be made, for example, red wine jus can be made by adding red wine instead of water.
Jus, veal or beef for example, can also be made by reducing veal or beef stock to thicken it and intensify the flavours. It should reduce down to a thick, sauce consistency.
Making jus or stock is a fairly long process, so best started at the beginning of the day, but good stock equals good flavour and is well worth the effort.
In the US you will find “au jus”, meaning “with the broth”. Sandwiches such as French dip are served with a bowl of the broth to dip the sandwich in, hence the name.