What type of database does CiviCRM use?
From CiviCRM Requirements

An installation of Drupal, Joomla or Wordpress, and the following additional requirements:

PHP 5.5+ is recommended. See the CiviCRM PHP Requirements page for details.
PHP memory_limit set to between 256 and 512 megabytes.  

MySQL 5.1.x or higher with INNODB support : CiviCRM is compatible with the current generally available MySQL release. Trigger support is required for logging and multi-lingual features. SUPER privileges are required in MySQL 5.1 if binary logging is enabled. 

Surprised if this (or other places which reference mysql) was hard for you to find, so please suggest where you think the documentation could be improved.