PDO stands for PHP Data Object. It is a lean and consistent way to access databases. It facilitates developers to write portable codes easily. PDO is not an abstraction layer. It is more like a data access layer which uses a unified API.
Drupal treats all the stored content on its web site as nodes. Any piece of content like blog, article, page, etc is considered as node. Although, the comments are not stored as nodes but they are always connected to a node.
DRUSH is a command line shell and UNIX scripting interface for Drupal.
The template.php file in the theme directory allows you to override a theme function.
Yes. Drupal can run on command line by using DRUSH.
Drupal integrates well with external search engines such as Xapian, Apache solr if the built-in search engine does not meet your needs properly.
Ctools is a set of APIs and tools which is used to improve the developer experience.
Hooks are Drupal API code which allows module to interact with Drupal core. Its module system is based on the hooks concept.
Render arrays are the basic building blocks in Drupal. They provide you a structured way to programmatically change the content before it is displayed.
There are three ways to interact with Drupal search system by implementing: nodeapi (update index) hook_search() hook_update_index()
