Seizure is the act of taking property. In the most common case, seizure occurs when law enforcement takes physical property into its possession, for example, if a police officer takes your money during a traffic stop. In the case of non-physical property, such as a bank account, seizure takes place when the law enforcement agency takes away your right to use the property. The seizure of a bank account, for example, takes place when you lose the right to use the money in your account.
Forfeiture occurs when your rights to the seized property are permanently lost through a court order or judgment. Forfeiture occurs after seizure, and seizure does not always end in forfeiture.
In our example, the seizure takes place when Officer Potts takes the money from Steve. Forfeiture takes place if, and only if, the Court rules that Steve’s money is contraband and that it will be forfeited. Then Officer Potts' police department gets to keep the money.