Meaning of ER in English

ER

ˈə(ə), ˈə̄(ə̄), ˈä(ä), ˈȧ(ȧ); the ˈər, usu prolonged, used by many R speakers when they encounter “er” as they read aloud is not an accurate reproduction of the sound that the spelling, introduced by -R speakers, is intended to convey interjection

— used to express hesitation

said shyly, “I — er — don't know”

Webster's New International English Dictionary.      Новый международный словарь английского языка Webster.