First let’s start with Ward Cunningham’s definition here.  The way I explained this at MADdotNET was poor at best.  ;)  While I tend to include measures of waste in technical debt, this is NOT generally shared by the Agile community.  Simply put, technical debt is the cost (debt) from hasty software design and development.  Steve McConnell expounds on this here.  I hope this clears things up!