Short Answer 
Chords are line segments with endpoints on a circle, while a radius connects the circle’s center to its circumference. The diameter is a special chord that passes through the center, being the longest chord, and differentiating between tangents (touching at one point) and secants (intersecting at two points) is essential for circle properties.
Step 1: Understand Chords and Radii
A chord is defined as a line segment with both endpoints located on a circle. It is important to note that a chord can never be classified as a radius. The radius connects the center of the circle to any point on its circumference, while a chord exists entirely within the circle without extending to the center.
Step 2: Recognize the Diameter
The diameter is a special type of chord that passes through the center of the circle, making it the longest possible chord. In terms of length, any chord will always be shorter than or equal to the diameter. Understanding that all diameters are chords helps to emphasize the distinction between these two terms.
Step 3: Differentiate Between Tangents and Secants
A tangent is a line that touches the circle at exactly one point, remaining outside the circle. In contrast, a secant is a line that intersects the circle at two points, thus extending through the interior of the circle. Recognizing these differences is crucial for understanding the unique properties of these lines in relation to a circle.