A Bin is a Dimension. Unlike Groups and Sets, Bins are based on a Measure. The purpose of Bins is to group the different values of a Measure in bins.
Bins have a special icon: 
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As always, the best way to understand is with examples. Let's create Bins with Sample Superstore:
- Right-click on Discount, navigate to Create, then click on Bins....
- A new window opens where you can edit the Bin. Keep the name Discount (bin). The size of the bin is automatically suggested by Tableau, but in our case, we want to see the reparation by 10%. Change the size of the Bin to 0,1. Here's how your Bin configuration window should look:
- Click on OK. A new Dimension is created. You should find the Bin in your data source, as shown in the following screenshot:
- Let's use it. Double-click on Number of Records, then on Discount (bin). You can now easily see that the majority of the orders have less than a 10% discount, or between 20% and 30%. Here's the final result:
With Groups, Sets, and Bins, we've seen three of the five field-creation capabilities. The last two, Calculated Field and Parameter, are even more interesting than those we just saw. But that's for Chapter 10, An Introduction to Calculations and Chapter 11, Analytics and Parameters.