Concept of Line

Line: A line is a straight path that extends infinitely in both directions and has only length, without width or thickness. 
Collinear points: If three or more points lie on the same line, they are called collinear points.

Non-collinear points: If three or more points don't lie on the same line, they are called Non-collinear points.
Concurrent lines: When two or more lines pass through the same point, they are called concurrent lines and the common point through which they pass is called their point of concurrence. i.e., point "O"

1. Representation of a Line:

• A line passing through two points, A and B is represented as ${\displaystyle \overrightarrow{AB}}$
• Similarly, a line passing through points P and Q is denoted as${\displaystyle \overrightarrow{PQ}}$

2. Properties of a Line:

• A line has only length and does not possess width or thickness.
• It consists of an infinite number of points along its path.

3. Determination of a Line:

• Two points are sufficient to define a unique line.
• This is expressed as "Two points determine a line."

4. Naming a Line:

• A line can be denoted using two points, such as AB or PQ.
• Alternatively, it can be represented by a single letter, such as l or m.