Sphere

1 curved face, there are no edges
Something is said to be spherical if it has the same shape as a sphere.

Hemisphere

This is half a sphere
For example cutting the world in 2 creates a northern hemisphere and a southern hemisphere

Ellipsoid

A sphere is based on a circle, while an ellipsoid is based on an ellipse.
An ellipsoid is a sphere flattened at the poles.
An ellipsoid has three pairwise perpendicular axes of symmetry which intersect at a center of symmetry, called the center of the ellipsoid.
If two of the axes have the same length then the ellipsoid is called a spheroid.

Ovoid

Egg-shaped; shaped like an oval, but more tapered at one end.