We have relatives such as elder brothers and sisters, aunts, or uncles, and they are called 大哥，大姐，大妈/大姨，or 大叔 in Chinese. Sometimes, someone you don’t know may call you 大哥，大姐，大妈，大叔 or 大爷，they do so just because ”大“ is used for respect or to be polite, e.g. when you ask someone older than you in the street for a favor, in order to be polite you can call him/her 大哥/大姐；soneone older than your parents, 大妈, 大姨/大叔，大爷. ”大“ can be used not only with people but also with things, such as 大作 your (esteemed) work, 大名 your (esteemed) name, etc.
You may also have interest in other posts about polite, courteous, honorific and humble.
