When two straight lines are plotted on the coordinate plane, we can tell if they are parallel from the slope, of each line. If the slopes are the same then the lines are parallel.
Parallel lines are two lines that are always the same distance apart and never touch. In order for two lines to be parallel, they must be drawn in the same plane, a perfectly flat surface like a wall or sheet of paper.
Parallel lines are useful in understanding the relationships between paths of objects and sides of various shapes. For example, squares, rectangles, and parallelograms have sides across from each other that are parallel.
In formulas, parallel lines are indicated with a pair of vertical pipes between the line names, like this:
AB || CD
Each line has many parallels. Any line that has the same slope as the original will never intersect with it. Lines that would never cross, even if extended forever, are parallel.
Mathematics is one of those subjects which you can easily spend hours studying but end up none the wiser. However much you have studied, if you cannot solve the problem on day of the test, you are lost. Thankfully, there are some techniques for studying mathematics that you can do regardless of your level.