An ersatz (German pronunciation: [ɛʀˈzats]) good is a substitute good, usually considered more expensive and/or of inferior quality to the good it replaces. It has particular connotations of wartime usage.
Ersatz is a German word literally meaning substitute or replacement. Although it is used as an adjective in English, it is a noun in German. In German orthography noun phrases formed are usually represented as a single word, forming compound nouns such as Ersatzteile ("spare parts") or Ersatzspieler ("substitute player"). While the term used in English often implies that the substitution is of unsatisfactory or inferior quality compared with the "real thing", it has both connotations in German, depending on the other noun; e.g. Ersatzteile ("spare parts") is a technical expression without any implication about quality, whereas in other cases it may mean things of poorer quality, e.g. Ersatzkaffee (coffee not made from coffee beans).
In the opening months of World War I, replacement troops for battle-depleted German infantry units were drawn from lesser-trained Ersatz Corps, who were less effective than the troops they replaced. Also, the Allied naval blockade of Germany throttled maritime commerce with Germany, forcing Germany to develop substitutes for products such as chemical compounds and . Ersatz products developed during this time included: synthetic rubber (produced from petroleum), benzene for heating oil (coal gas), tea composed of ground raspberry leaves or catnip, and coffee substitute using roasted acorns or beans instead of coffee beans.