it simply means 'house' but it can also mean things figuratively. the word used for house normally is σπίτι. Οίκος can mean 'house' in the sense of dominion or property, or it can simply refer to a building. Think 'household' or even 'family', the prefix eco- for words like 'economy' and 'ecology' comes from οικος. It's not, however, the everyday, simple word for 'house'.