Gmail Plugin

A plug-in or add-in / addin, plugin, extension or add-on / addon is software that adds a specific feature to an existing software application. 

When an application supports plug-ins, it enables customization.

Gmail Plugins

• FullContact - shows all the information about my contacts: social media profile, photo, real name, etc.  It allows the user to know who I am talking to and helps with relationship building.