K is the chemists abbreviation for potassium (Na is sodium)
meta is a short cut for metabisulphite
So K-meta is potassium metabisulphite. It is the active ingredient in most campden tablets.
Uses....
1) clears your sinuses (in an industrial strength kinda way)
2) stuns yeast and some bacteria (note contrary to popular opinion it does not kill yeast)
3) anti-oxidant to lengthen the shelf-life of finished wine.
Do not confuse with potassium sorbate. Under the right conditions that will stop the yeast from reproducing, in essence shutting down fermentation.
Steve