Scratchpad is one of those
words we use very often in our
communication but is not considered part of regular
vocabulary.
In day-to-day life, its a sticky note at times. A regular but rough usage small sized paper pad often.
But to me, one of the main requirements of any practical scratchpad is the ability to be wiped clean and reused. To this effect, programs like handwrite for palm fit my personal definiiton like a glove.
In computer jargon - scratchpad is used (not very commonly though) for a high-speed internal memory used for temporary storage of preliminary information. (According to WordNet ® 1.6, © 1997 Princeton University)