Wa 3alaikoumou salam wa Rahmatoullah wa Barakatouh,
Barakallahou fikoum for your answers
Oum means "mother". It's a simple nickname. In certain muslim countries (as Bahrein, Liban,...), brothers and sisters don't give their real name (for example, when they ask questions to a cheikh on telephone, in the street!...), so they give a nickname begining with "Oum" or "Abou".
Wasalamou 3alaikoum wa Rahmatoullah wa Barakatouh