Answer:
A key field is used to uniquely identify each record for retrieval or manipulation.
Explanation:
In a database there are many, having similar entities. So in order to differentiate each entity from other we need to set a key field among all the field which is always unique for each entity.
For example:
In a database of a company having data about its employees, the key field might be their ID. As some employees can have same names, addresses, phone numbers but cannot have the same ID.
