Tabitha defines a sphere as the set of all points equidistant from a single point. is tabitha's definition valid?

Answer
YES it is VALID.

Explanation.
In 3 dimension, it can be seen that a sphere is a round solid. It is a round object where the distance from the centre to every point on the surface is equal.
Tabitha says that a sphere is a set of all points equidistant from a single point. This single point must be the centre of the sphere for that definition to be true. This definition is correct. 

Yes, Talid's definition is valid.

Step-by-step explanation:

Definition of sphere:- In geometry , a sphere is a perfectly round three-dimensional shape . It is defined as the set of points that are all at the same distance which is known as radius from a given point in a 3-dimensional space. Talid's definition:- A sphere as the set of all points equidistant from a single point.

Hence, Talid's definition is valid.