What is difference between a feeder and transmission line?

Consider a  distribution substation  which receives power from a transmission line.
To connect the consumer/load end with the substation , we have feeders. There are no tapping taken out of them. They just connect the consumer area with the substation.
As pointed out in other answer , a transmission line is called a feeder whenever it directly feeds consumer.

Transmission lines are current carrying lines that carry power from generating stations to the substations.

Feeder is an electrical distribution network. They carry power from substation to consumers .

A feeder is line which starts from grid to whom which we want to transmit power to the consumers.

A transmission is a line starts from generating station and ends at the power grid . it can be either short ,medium, or long transmission line.