Cheie means key in the singular.
Its plural is chei = keys.
Romanian usually adds the definite article to the end of the noun, instead of putting a separate word like the in front.
So:
This ending -le is the definite article here.
Because mele agrees with a plural feminine noun.
Romanian possessive words change depending on the gender and number of the thing possessed:
Since chei / cheile is feminine plural, you say:
You usually learn the noun together with its gender. In this case, cheie is a feminine noun.
You can see it from forms like:
The possessive mea / mele also shows that the noun is feminine.
This is the normal and natural Romanian word order for a simple question:
So literally: Where are my keys?
Romanian often uses this same pattern in questions with unde:
You could sometimes change word order for emphasis, but Unde sunt cheile mele? is the standard form.
Both are correct, but they mean slightly different things:
If it is already obvious whose keys you mean, Romanian speakers may sometimes leave out the possessive. But if you specifically want to say my keys, keep mele.
A helpful approximation is:
More carefully:
So cheile is about KAY-leh, with a slight extra vowel transition: KAY-eh-leh.
Also:
So cheie does not sound like English chewy or chay with a ch sound.
Yes, sunt is the normal present plural form of to be for we/you plural/they in standard Romanian.
Examples:
In your sentence, sunt means are because the subject is plural: cheile mele.
Yes. Unde-s cheile mele? is a common shortened spoken form of Unde sunt cheile mele?
Here:
This is natural in conversation, but in learning materials and careful writing, you will usually first see the full form Unde sunt cheile mele?
Because Romanian usually uses a postposed definite article, meaning the definite article is attached to the end of the noun.
Compare English and Romanian:
So instead of saying a separate word like the, Romanian modifies the noun itself.
That is why cheile mele literally looks something like keys-the my, even though the natural English translation is my keys.
The singular version is:
Unde este cheia mea?
Breakdown:
So: