IPA: /ˈɛk.sə.nɪm/
KK: /ˈɛksoʊnɪm/
A name that one group of people uses to refer to another group, which the second group does not use for themselves.
The term 'Germany' is an exonym used by English speakers for the country that its inhabitants call 'Deutschland'.
Exonym → It is formed from "exo-" (from Greek "ἔξω" meaning outside) and "-onym" (from Greek "ὄνυμα" meaning name). An exonym refers to a name used by outsiders to refer to a geographical place or group, as opposed to the name used by the locals.
Think of 'outside' ('exo-') and 'name' ('-onym') to remember that an exonym is a name used by outsiders for a place or group.