Honorific Prefixes
The bikago (beautifying) prefixes o- and go- (both written 御, or in hiragana) are honorific prefixes which are applied to nouns and in some contexts to verbs. In general, go- (the on'yomi) precedes Sino-Japanese words (that is, words borrowed from Chinese or made from Sino-Japanese elements), while o- (the kun'yomi) precedes native Japanese words. There are many exceptions, however, where the o- prefix is used for Sino-Japanese words, including お茶 o-cha "tea", お大事に o-daiji-ni "get well", お電話 o-denwa "telephone", お稽古 o-keiko "practice", and many others.
These prefixes are used for two purposes: to speak respectfully about a social superior's family, belongings, or actions (as part of 尊敬語, sonkeigo); or to speak in a generally refined or polite way (敬語 keigo generally, specifically 美化語, bikago).
Read more about this topic: Honorific Speech In Japanese