I am building my very own nav menu using custom taxonomies and also the get_groups() method and that i notice when I am attempting to pull my link for that category I'm able to choose from cat_id and term_id. It is possible to distinction between the 2? Which must i be utilising?

Here's a good example of my code while using term_id

foreach ($subcategories as $subcategory) {
    $output .= '<li><a href="'. get_category_link($subcategory->term_id) .'">' . $subcategory->name . "</a></li>\n";

In a nutshell, taxonomy was added since WordPress v3. and it is a grouping mechanism.

The very best and many comprehensive answer I possibly could find comes from the Codex itself: http://codex.wordpress.org/Taxonomies#What_is_a_taxonomy.3F

To reply to your question about which you ought to be using, each one can function, it will depend somewhat in your use of it.

Consider Stack Overflow's tags for the reason that when you initially publish an issue, place the as numerous tags in as you would like a moderator or perhaps a user with sufficient status might arrive and edit it and take away tags. Why? It's often because new tags may have no fans yet and altering or adding give a tag which has a lot of fans means you will see a larger likelihood that the question can get clarified by your customers.

The 2 mean exactly the same. Term_id may be the actual area title within the wordpress_terms database table, cat_id is really a frontend abbreviation, possibly easier understood by individuals working in the front-end only.