What is the meaning of оу?

A letter of the Old Cyrillic script, called uk or digraph uk.

A letter of the Old Church Slavonic alphabet, called оукъ (ukŭ) and written in the Old Cyrillic script.

from

at

in

A letter of the Old Novgorodian alphabet, written in the Old Cyrillic script.

at, near [with genitive]

The name of the Latin script letter O/o.

ow, oh

Source: wiktionary.org