A chord is a line segment whose endpoints lie on a circle. A secant is a line (or line segment) that intersects a circle in two places, endpoints NOT on the circle.
Yes but only if it's an equilateral or an isosceles triangle otherwise it's the vertical perpendicular height
This segment would be the radius of a circle.
It's called a chord.
A segment whose endpoints are points on the sphere.
That's a "chord" of the circle.