An entity that has attributes could be a candidate for a class or in other words attributes of an objects are called Candidate for a class.
Take an example of address where we have Street name, City, State, Zip Code, and Country. Now we will have a seperate class for them is Address Class.
Now each item of the address section in the registration form could be treated as an attribute of the AddressClass. Again items like city, state and country could be objects themselves. If each of these items could have more than one attribute, then they could become candidates for objects.