Singulation is a method by which an RFID reader identifies a tag with a specific serial number from a number of tags in its field. This is necessary because if multiple tags respond simultaneously to a query, they will jam each other. In a typical commercial application, such as scanning a bag of groceries, potentially hundreds of tags might be within range of the reader.
Read more about Singulation: Collision Avoidance, Tree Walking, ALOHA, Slotted Aloha, Listen Before Talk