To stand up for somebody is to defend a person or an idea under attack. Stand up for yourself, stand up for a friend, stand up for what is right.
It implies a cost, since the defender risks something by speaking. The picture is literal, from rising to your feet to speak when others stay seated.
1phrasestand up forTo defend a person or idea under attack.
“Somebody had to stand up for the youngest of them.”
stand up for is a phrase.
Practised in Phrasal Verbs