How to create something like a textual "add other term" for taxonomy terms? How can I setup taxonomy terms so that you can have an extra field called "others", where you can add your own terms if the term you want to use is not defined yet as a term of that taxonomy?

I have researched and came across a module called Select(or other). It does what I want, but it is in text.

My problem now is that I've added so much taxonomies for my student record content type (like countries, or faculties). So I've gone too far and cannot cancel (undo) the taxonomies and replace them with the module I found.

Any suggestion of how to add something like such extra field to the existing taxonomy module?

I imagine that when users insert data, they might not find appropriate terms to choose from. So I want to give them an option that "if current term don't apply to you, then please insert your term manually".

I'm still newbie in Drupal7 and PHP programming.
When you go to your Taxonomy Vocabulary ([your_domain]/admin/structure/taxonomy/your_vocabulary) you can click on Manage Fields tab and add any field you want. Or go to [your_domain]/admin/structure/taxonomy/your_vocabulary/fields.