过去 (guòqù) is the standard, everyday noun for 'the past; former times'. It is more common in speech than 以往 (yǐwǎng, more formal/literary) and 过往 (guòwǎng, even more literary). Note that the same characters also form a verb 'to go over' (guòqu, neutral tone), but this HSK3 entry is only the noun.