Meaning of ER in English

ER

er /ɜː, ə $ ɜːr, ər/ BrE AmE interjection British English

[ Date: 1800-1900 ; Origin: A representation of the sound ]

a sound you make when you do not know exactly what to say next:

Well, er – I’m not really sure.

Longman Dictionary of Contemporary English.      Longman - Словарь современного английского языка.