Do all lines with the same slope have the same line?

No, not necessarily. They could have different y intercepts.

For example, take one horizontal line, and another horizontal line.

These horizontal lines would both have the same slope, 0. But one could be higher up, or have a higher y intercept, than the other.

They would still have the same slope, but not be the same line.

The major difference is that a histogram is only used to plot the frequency of score occurrences in a continuous data set that has been divided into classes, called bins.  bar charts, on the other hand, can be used for a great deal of other types ofvariables  including  ordinal  andnominal  data sets.