'Frankenstyle' refers to the naming convention that is used to uniquely identify a Moodle plugin based on the type of plugin and its name.

Martin Dougiamas is credited with inventing the word 'frankenstyle'. (It is a great word!)

Format

Frankenstyle names have a prefix and then a name, separated by an underscore.

The prefix is determined by the type of plugin. For example, the prefix for an activity module is mod.
The name is the name of the plugin. (Plugin names are always made of lower-case letters.)

So the frankenstyle name for the quiz module is mod_quiz.

Plugin types

Activity modules: [mod] => /mod
Admin reports: [report] => /admin/report
Assignments: [assignment] => /mod/assignment/type
Authentication plugins: [auth] => /auth
Blocks: [block] => /blocks
Course formats: [format] => /course/format
Course reports: [coursereport] => /course/report
Database field types: [datafield] => /mod/data/field
Database presets: [datapreset] => /mod/data/preset
Editors: [editor] => /lib/editor
Enrolment plugins: [enrol] => /enrol
Filters: [filter] => /filter
Grade export plugins: [gradeexport] => /grade/export
Grade import plugins: [gradeimport] => /grade/import
Grade reports: [gradereport] => /grade/report
Local plugins: [local] => /local
Messaging consumers: [message] => /message/output
Mnet services: [mnetservice] => /mnet/service
Plagiarism plugins: [plagiarism] => /plagiarism
Portfolio plugins: [portfolio] => /portfolio
Question behaviours: [qbehaviour] => /question/behaviour
Question formats: [qformat] => /question/format
Question types: [qtype] => /question/type
Quiz reports: [quiz] => /mod/quiz/report
Repository plugins: [repository] => /repository
SCORM reports: [scormreport] => /mod/scorm/report
Themes: [theme] => /theme
User profile fields: [profilefield] => /user/profile/field
Webservice protocols: [webservice] => /webservice
Workshop allocation strategies: [workshopallocation] => /mod/workshop/allocation
Workshop evaluation plugins: [workshopeval] => /mod/workshop/eval
Workshop grading forms: [workshopform] => /mod/workshop/form

To get a definitive list, do print_object(get_plugin_types()); in a Moodle 2.x install.

Frankenstyle is used in:

All table names for a plugin must begin with its frankenstyle name (after the standard Moodle table prefix).

Examples: mdl_mod_quiz, mdl_mod_quiz_attempts

All capabilities for a plugin use the frankenstyle name, except with a / instead of a _.

Example: mod/quiz:viewattempt

Please add more as they come up.