The definition of Civil Asset Forfeiture from Wikipedia:
Civil forfeiture in the United States, also called civil asset forfeiture or civil judicial forfeiture[1] or occasionally civil seizure, is a controversial legal process in which law enforcement officers take assets from persons suspected of involvement with crime or illegal activity without necessarily charging the owners with wrongdoing. While civil procedure, as opposed to criminal procedure, generally involves a dispute between two private citizens, civil forfeiture involves a dispute between law enforcement and property such as a pile of cash or a house or a boat, such that the thing is suspected of being involved in a crime. To get back the seized property, owners must prove it was not involved in criminal activity.
In all other aspects of our jurisprudence the citizen is innocent until proven guilty. Until it comes to that one thing the goddamned government loves above all other things: money. So they just made themselves this little exception to the 4th Amendment and told us to go f--k ourselves if we don't like it. Both the Democrats AND the Republicans love this. In fact only one political party in all the land of the free has fought against this legalized theft: http://www.lp.org
An example. Driving down the road with 100.000 in cash, being stopped by the police who seize your money on suspicion that you acquired it illegally. You now have the burden of proof that you are not a drug dealer. How exactly would you do that. The truth might not be good enough.