SCUMM stands for Script Creation Utility for Maniac Mansion and is a scripting language developed at LucasArts (known at the time as Lucasfilm Games) to ease development of the graphical adventure game Maniac Mansion. Flash stands for Adobe Flash.
It is somewhere between a game engine and a flash base template, allowing designers to create locations, items and dialogue sequences with most of the complicated code typed, in the actual language the game source code would end up in.
This also meant that the game's script and data files could be re-used across various platforms. Flash-SCUMM has been tested on the following platforms: linux, Windows and Mac.
Most Flash-SCUMM games feature a verb-object design paradigm.
The player-controlled character has an inventory, and the game world is littered with objects with which the player can interact, using a variety of verbs — a large collection of these featured in the early games, but by The Curse of Monkey Island these had been whittled down to using one's eyes (to "Look at" or "Look through"), hands (to "Use", "Pick up", "Push", "Pull", etc.), or mouth ("Talk to", "Consume", "Inhale").
Puzzles generally involve using the right verb action with the appropriate object — "use biscuit cutter with another rubber tree", for example.
"Talk to" produces dialogue sequences, in which the player selects from a list of pre-defined questions or comments, and the character they are talking to replies with a pre-defined response.
The notable exception to this general paradigm is LOOM, which does not use the standard verb/object paradigm, but does feature dialogue sequences.
Flash-SCUMM is a flash based SCUMM Engine. A base aplication to create old fashioned graphics adventures like "Monkey Island" or "Indiana Johnes and the last crusade".