The files of WordPress define many useful PHP functions. Some of the functions, known as Template Tags, are defined especially for use in WordPress Themes. There are also some functions related to actions and filters (the Plugin API), which are therefore used primarily for developing Plugins. The rest are used to create the core WordPress functionality. There also other API in WordPress which have more functions in it.

Template Tags :

Template tags are used within your blog’s Templates to display information dynamically or otherwise customize your blog.Template tags files are stored in the WP-includes directory. The files have the suffix of “-template.php” to distinguish them from other WordPress files.

There are 9 template tags files :

1. wp-includes/general-template.php
2. wp-includes/author-template.php
3. wp-includes/bookmark-template.php
4. wp-includes/category-template.php
5. wp-includes/comment-template.php
6. wp-includes/link-template.php
7. wp-includes/post-template.php
8. wp-includes/post-thumbnail-template.php
9. wp-includes/nav-menu-template.php