One of the nicest features of Drupal’s taxonomy module is the “Tag” option; users can enter their own tags, separated by commas, and the terms are automatically added to the vocabulary if they don’t already exist. On a recent project, we were setting up a free-tagging vocabulary for law firm names. In our testing, we encountered firms with a name like Doe, Johnson, & Smith that would, unsurprisingly, create three terms when entered: “Doe”, “Johnson”, “& Smith”. 

After some more testing, I found that you can enter terms with commas in them by placing them in double quotes. So if you wanted to enter a term with commas in it, place double quotes around your term like this: “Doe, Johnson, & Smith”.  When you save the term, you should have a single term instead of the term being split into multiple smaller terms.