There are a number of obscure abbreviations and code names in the source code, directory paths, file name suffixes, etc. The purpose of this document is to dispel confusion by defining them.

apk (Android package)

a compiled application capable of being installed on an Android device.

blk

a file name suffix for the user source code created in the Blocks Editor; component information is in a corresponding "scm" file.

GWT (Google Web Toolkit)

a set of tools for creating client-server applications whose front-end runs as Javascript in the client browser and whose back-end runs as compiled Java on a server.

ode (online development environment)

a general term for a programming environment run as a client-server application, rather than locally.

repl (read-eval-print loop)

the code enabling changes to App Inventor programs to be immediately visible on a connected device.

scm

a file name suffix for either (1) Scheme code in the source repository or (2) component information for a user project (an accompanying "blk" file holds user source code).  It is an unfortunate historical accident that the same suffix is used for two unrelated file types.

Simple

a simple programming language whose source code was incorporated into App Inventor.

yail (yet another intermediate language)

Scheme code produced when compiling a project, or the suffix of the name of a file containing such code.

youngandroid

the original internal name of App Inventor.