The word 'lines' usually refers to a 'straight line'. It has no width.It has just length. It is absolutely straight and can extend indefinitely in both directions.
There are different types of lines. 1) Vertical 2) Horizontal lines 3) Intersecting 4) Coplanar 5) Skew 6) Parallel 7) Transversal 8) Concurrent
1) Vertical line : A vertical line is one which runs up and down the page.
2) Horizontal line : A horizontal line is one which runs left-to-right across the page. It comes from the word 'horizon', in the sense that horizontal lines are parallel to the horizon.
A vertical line is perpendicular to a horizontal line.
3) Intersecting lines : When two lines cut each other at one point. Such lines are called intersecting lines. The meeting point of two lines is called the point of intersection.
Here, the lines l and m are intersecting lines and O is the point of intersection.
4) Coplanar : The lines which lie in the same plane are called coplanar lines.
The lines l,m and n lie in the same plane so they are coplanar.
5) Skew lines : The two or more non-coplanar lines which do not intersect each others are called skew lines.
Here, lines p and q are skew lines as they both lie in two different planes.
6) Parallel lines : Lines are parallel if they are always the same distance apart (called "equidistant"), and will never meet or never intersect each other.
Just remember: Parallel lines are always the same distance apart and never touch each other.
The line 'l' and 'm' are parallel lines. It is denoted as l || m.
7) Transversal : The line which cut the parallel lines in two points is called transversal. It is generally denoted by 't'.
Here, line l and m are two parallel lines and 't' is the transversal as it cuts the two parallel lines in two points A and B.
8) Concurrent lines : When two or more coplanar lines( lying in the same plane) intersect each other in one point, such lines are known as concurrent lines. The intersection point is known as the point of concurrence.
Lines l, m and n intersect at point O, so O is known as the Point of concurrence. Basic Geometry