sometimes
The greatest number is six.
Not necessarily, eg the three points (0, 0), (1, 1) and (2,0) are not co-linear, but (0,0), (1,1) and (2,2) are. But three points are co-planar, that is they all lie in one plane.
Yes, three points define a plane. So any three points lie in some specific plane and are therefore co-planar.
They are coplanar if the line joining any two of them intersects the line joining the other two.
Yes. A circle is defined as the set of all points in a plane equidistant from a given point (the center of the circle) - hence - all points of a circle must be co-planar by definition.
co-planar
Co-planar means being in the same plane.
co-planar
Parallel lines will be co-planar.
The difference is that one is co-linear force is one dimensional and co-planar force is 2-dimensional. Co-linear force is the force which is acting along a single line, whereas co-planar force is the force which is acting along a single plane.
They never touch but they are not parallel because they are not co-planar