On Instagram, "su" typically stands for "shoutout." It is often used when users promote someone else's account by recommending them to their followers. This can be part of a shoutout-for-shoutout (S4S) arrangement, where two users agree to share each other's profiles to gain more visibility and followers.
SU means WITH
His as of his pants '' su pantalon''
Su autorización - Its okay
Su hyun
It can mean "your" (formal) or his, or her.
"Su casa" means "your house."
"Su hermana" means "his/her sister" in English.
"Su amigo Pedro" means "his/her friend, Pedro"
Estoy a su bebe in English means I am a baby.
"Su mano derecho" means "his/her/your right hand."
"Su hermano" in Spanish means "his brother" or "her brother," depending on the context in which it is used.
While some people refers it to InstaGram. The most common acronym for InStaGram is "Insta" or "ISG".