Coincidental lines are any lines that have the same slope and $y$-intercept. Coincidental lines intersect at every point because they lie on top of one another. The name coincidental lines comes from the word coincide, which means to exist together or occur at the same time. For example, the lines $y=2x+1$ and $2y-4x=2$ coincide and are, therefore, coincidental.

Even though coincidental lines are essentially the same line, they can have different equations when written in standard or point-slope form. However, they will always have the same equation in slope-intercept form because their slopes and $y\text{-}$intercepts are equal.