Hint: In all branches of mathematics, there are some of the fundamental pieces which cannot be and not needed to be defined. As they are used as building blocks of definition for other objects and more complex pieces. In geometry, there are three undefined terms and are the underpinnings of Euclidean geometry.
Complete step-by-step answer: Here, in Euclidean geometry, we have in total three of the undefined terms i.e., which need not to be defined in a separate manner, despite they are used to define other complex pieces. The three undefined terms of geometry are: 1.Point 2.Line 3.Plane For instance, Point cannot be defined in particular but can be used to define any of 2D or 3D objects in cartesian space like a triangle, a line segment, or a cube. Similarly, Line is just another collection of points arranged in a particular pattern which is further used to define other more complex objects like a wire. While, a Plane is again just a collection of lines in a particular space and direction like a land. Hence, the main three undefined terms of geometry are Point, Line and Plane.
Note: It might seem to be a basic thing but usually undefined terms can easily be confused with fundamental things like, a triangle which is nothing but a closed figure with three sides, etc.
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