Русско-англо-русский юридический словарь

As an example, if you go into a pub and ask for a pint of beer and the barman says "certainly sir", at that point there is a contract of sale but you are not the owner of any part of the beer in the barrel. But when the barman fills a glass for you at that point the beer is appropriated to the contract of sale and becomes your property. The beer has been appropriated to the contract by the seller with the assent of the buyer.

On the other hand if the barman says "certainly sir but I am a bit busy right now so would you mind coming round this side of the bar and filling a glass from the barrel yourself" that means that the beer has been appropriated to the contract by the buyer with the assent of the seller.

So it means that the goods are designated or destined to the contract, i.e. that they have been designated to be given to the buyer in fulfillment of the contract. (StackExchange)