plug-in

[pluhg-in] /ˈplʌgˌɪn/
adjective
1.
capable of or designed for being connected to an electrical power source by plugging in or inserting:
a plug-in hair dryer; a plug-in transistor.
noun
2.
plug (def 3).
3.
jack1 (def 3).
4.
a plug-in appliance.
Origin
1920-25; adj., noun use of verb phrase plug in
Word Origin and History for plug-ins

plug-in

adj.

1922, from plug (v.) + in (adv.).

plug-ins in Science
plug-in
  (plŭg'ĭn')   
An accessory software or hardware package that is used in conjunction with an existing application or device to extend its capabilities or provide additional functions.