RANKING: Why is my page ranking for keywords I haven’t used?

Google is getting smarter and smarter. It makes word associations so if your page is targeting ‘flight costs’ – Google will make an assumption that it’s probably relevant for people searching for ‘flight prices’, ‘costs of flights’ etc. Remember that Google is trying to think about User intention. The user intention is the same for all the phrases above, they want the same thing, so even though you haven’t used this exact phrase in your page, you may in fact rank for it.