It could be solid but it need not be: for example, it could be a wriggly line drawn on the surface of a sphere.
A point
a rectangle
In a close figure it is the set of points inside the figure.
The space within an object is its volume.
The geometry of similarity in the Euclidean plane or Euclidean space.
a figure that is used in geometry
A point.
A point
a rectangle
They can be any figure
In a close figure it is the set of points inside the figure.
The space within an object is its volume.
A straight line is a one dimensional figure in geometry
The geometry of similarity in the Euclidean plane or Euclidean space.
Geometry
According to geometry, a quadrangle is a figure having four angles and four sides.
Hyperbolic geometry is used very often in space, such as space travel and gravitational pulls and rotations of planets. This geometry is used most often in space because of Einstein's general Theory of Relativity assumes that space is not a Euclidean space, but a hyperbolic one.