It's the posh pronunciation of the word cache, which other folks pronounce as "cash". It refers to a temporary storage unit, for example, in the browse software on your computer if, you do a 'hard refresh' (Ctrl+F5 on Windows) it will refresh your cache, so the images, scripts and stylesheets are regenerated afresh. Or when living in the wilderness, you may hide something underground or in a secret place among vegetation - this would be a geocache.