Lightbox libraries are used to display images, videos, iframe and other content in an overlay above the website page by dimming out rest of the web page.
Here is a list of 7 best Drupal modules that integrate various lightbox libraries into Drupal.
Colorbox is a light-weight customizable lightbox plugin for jQuery. This module is also available for Drupal 8.
The Lightbox2 module is a simple, unobtrusive script used to overlay images on the current page.