Capable of being plugged, or plugged in, especially in reference to optional components of software(adjective)
Wiktionary.org : Text is available under the Creative Commons Attribution-ShareAlike License
Use "pluggable" in a sentence
"Drupal has a base setup that can be expanded by "pluggable" modules."
"All switches are front panel "pluggable", and when combined with the built-in relay odometer, facilitate quick field maintenance and service activities."
"Notable new features are: better Unicode support, proper support for time after the Y2038 barrier, new APIs to allow developers to extend Perl with 'pluggable' keywords and syntax, warnings for deprecated features and more."