I've been involved in many cases that include a civil forfeiture aspect, both as a prosecutor and a defense attorney. Put simply, civil forfeiture is where the police seize property because they think it has been used in a crime. The onus is on the owner of the property to prove their innocence or else the property is forfeited (turned over) to the government. As found in Reason magazine:
Under civil forfeiture, police can seize property from people who are never convicted—much less charged with—a crime. Unlike criminal forfeiture, where the government must prove property was used in the commission of crime, civil forfeiture law presumes an owner’s guilt.
Civil forfeiture is a national problem. Law enforcement agencies seize millions of dollars worth of property each year with little or no due process for owners. In all but six states property owners are considered guilty until proven innocent. State law typically allows law enforcement to keep most or all of the proceeds from forfeiture—an enormous incentive to police for profit.