Depending on your requirements you may need to assign metadata to a folder. At first I thought it would be fairly straight forward but realized it required a few very specific steps in order to accomplish this task.
Step 1: Go to a Document Library that has a Managed Metadata Column and create a folder
Step 2: Click on the Library tab and select the Quick Edit icon
Step 3: Click into the metadata column and type in your Metadata Value and then click on “Stop” to stop editing the list