Step 1: Understanding the Question:
The question asks for the specific term used in mechanics to describe a system of forces where all the forces' lines of action intersect at a single, common point.
Step 2: Detailed Explanation:
Let's define the terms given in the options:
Parallel Forces: The lines of action of these forces are parallel to each other and never intersect.
Coplanar Forces: These forces all lie within the same two-dimensional plane. Their lines of action may or may not intersect at a common point.
Concurrent Forces: These are forces whose lines of action all pass through a single common point. This matches the description in the question perfectly.
Collinear Forces: These are forces that act along the same straight line. They are a special case of concurrent forces.
Step 3: Final Answer:
The definition that exactly matches the condition "line of action passes through a common point" is Concurrent Forces. Therefore, option (C) is correct.