The mass of a single bead for instance. If you were interested in the mass and the thickness of each bead then you would be collecting 2 dimensional data. If you find the mass, length, and chemical composition of each bead then you have three dimensional data. In each case there are different techniques for presenting and analyzing the data points. A particular kind of plot called a histogram is a classic way of presenting 1 dimensional data.
Histograms show how many data points fall in a particular range of values.
This is sometimes called a frequency plot. A histogram that you have all seen is the plot that shows how many students got what grades on a test. As you can see in the following examples the height of the bar indicates how many students received grades in the indicated range. You will note that how I choose to divide up the range significantly affects the usefulness of the plot. Think about how you perceive these differences.