# Elliptic Curve on FF points are expressed as 3 numbers?

Why are elliptic curve points defined as 3 numbers? As in the following sage snippet:

```
sage: e = EllipticCurve(GF(13),[0,1])
sage: e.points()
[(0 : 1 : 0), (0 : 1 : 1), (0 : 12 : 1), (2 : 3 : 1), (2 : 10 : 1), (4 : 0 : 1), (5 : 3 : 1), (5 : 10 : 1), (6 : 3 : 1), (6 : 10 : 1), (10 : 0 : 1), (12 : 0 : 1)]
```

I looked at the official sage documentation here and can't seem to find an answer. What does each number in the point represent? X,Y and something else I assume.

I don't have a strong background in abstract algebra/number theory so forgive me if this is something obvious.