This is a legal regulation that allows people who are approved adopters to also be approved short-term as foster carers. They will only be approved for a specific named child. This enables the child can to be placed with them under a fostering for adoption arrangement.
In such cases, the expectation is that the approved adopters will usually go on to adopt the child. This does not happen in every case. Sometimes the child will move to live back with their birth parents or another relative.
As they will have already been approved as an adopter, there is no requirement for these people to go through the full fostering assessment process. This is because they will have already been through a thorough adoption approval process.