Brown sauce (bottled) of one kind or another is often seen on the tables of most British cafes and has a certain popularity in other countries. It is a commercial descendent of the home-made ketchup of earlier times, and also related to Worcester sauce which is, however, much more concentrated, and a condiment rather than a relish.It bet it's the gummy texture that makes it so good. That last bit about these being different from any brown sauces in French cuisine didn't even have to be stated, did it? I think we all knew that already.
Brown sauces come in bottles of various shapes, and bear labels which make interesting reading for connoisseurs of food additives. They combine sweet, vinegary, and spicy elements, and often have a gummy texture.
The best-known variety is HP sauce. HP stands for the Houses of Parliament, in whose members' restaurant it is fact available. Its history is the subject of an interesting book by Landen and Daniel (1985). As this book explains, many other memorably named brands have come and gone, or survive.
The brown sauces (sauces brunes) of French cuisine are an entirely different matter.