Definition of Triangle:
A triangle is a closed two-dimensional shape with three straight sides and three angles. It is one of the basic shapes in geometry, characterized by having three vertices and three edges.

Key Points:
- A triangle is always formed by three line segments that connect at three non-collinear points.
- The sum of the interior angles of a triangle is always 180 degrees.
- Triangles can be classified based on the length of their sides (equilateral, isosceles, scalene) and the measure of their angles (acute, obtuse, right).

Figure of Triangle:
A triangle can be represented visually as a shape with three sides and three angles. It can have various orientations and sizes, but the fundamental structure remains the same with three vertices and three edges connecting them.
The figure of a triangle is typically denoted by drawing three line segments connected at their endpoints to form a closed shape. The angles formed at the vertices are labeled accordingly, and the sides may be of equal length in the case of an equilateral triangle or have different lengths in the case of a scalene triangle.
Triangles are essential in geometry and have various applications in mathematics, engineering, architecture, and other fields. They serve as the building blocks for more complex geometric shapes and concepts, making them a fundamental element to study and understand in mathematics.