Drupal

• Allows (fieldable) entities to be translated into different languages.
• Entity Translation provides field-level translation, so that site builders can select which fields should be translatable.
• It provides a UI for users to translate these field into other languages
• Entity  translation is now in Drupal 8 core.
• It is not a replacement for the Internationalization (il8n) package.

• PDO means PHP Data Object; it is a lean and consistent way to access databases. It allows developers to write portable code with ease.
• Drupal provides a data abstraction layer to provide developers with ability to support multiple database servers easily.
• The intent of this layer is to preserver the syntax and power of SQL as much as possible, but also allow developers a way to leverage more complex functionality in a unified way.

You use helper functions such as module_invoke_all(), module_invoke(), drupal_alter() to invoke all functions matching the expected name pattern. 

These invoked functions are usually found with module_implements()

the best practices to document them in module.api.php by creating empty stubs hook_name function.

A Patch is a file that contains a list of differences between one set of files and another.
Through patches, all the changes in code like additions or deletions to Drupal core can be made.

Perform setup tasks for non-cached page requests.

hooks are drupal API code which allows module to interact with the Drupal core.

Provide tools for running a group of affiliated sites from one drupal installation and single shared database.

* backing up the site,
* putting it into maintenance mode
* downloading the new version of the module
* uncompressing it
* running update.php
* testing the site
* taking the site out of maintenance mode

Drupal is a Content Management System(CMS). It's an open source content and free CMS framework written in PHP. It enables you to organize, manage and publish content with ease and comes with a variety of customization option.

Drupal is free, open source software that can be used by individuals or groups of users  to easily create and manage many types of Web sites. The application includes a content management platform and a development framework.

A brief history of content management
  > Content management systems like Drupal are traditionally monolithic.
  > In traditional monolithic CMS architectures, the CMS provides soup-to-nuts feature sets.
  > This includes server-side templating, and all markup is controlled by a server-side language.