Histogram vs Frequency Polygon
Both terms below come up in the same part of the course, and students mix them up. Here is each one defined on its own, side by side, so you can see where they part company.
Histogram
Graphs and displays
A histogram displays quantitative data by grouping values into equal-width intervals and drawing a bar for the count in each interval.
A histogram divides the number line into bins of equal width and draws a bar whose height is the frequency in that bin. For example, exam scores might be binned as 60 to 70, 70 to 80, and 80 to 90, with bar heights giving how many scores land in each. Unlike a bar graph, the bars touch because the horizontal axis is a continuous number scale. The bin width you choose affects how smooth or jagged the shape looks.
Frequency polygon
Graphs and displays
A frequency polygon is a line graph of a frequency distribution, made by connecting points plotted above each histogram bin's midpoint at the bin's height.
A frequency polygon carries the same information as a histogram but draws it as a single line, which makes two distributions easy to overlay on one set of axes. Each point sits above the midpoint of a bin, at a height equal to that bin's frequency. For example, a bin covering 60 to 70 that holds 8 values contributes the point , because the midpoint is . The line is usually anchored down to zero at an empty bin on each end so the polygon closes onto the axis.