What is the/a identifier variable?

The Data is shown here
Variable Name Description of Variable
name - full name of the passenger,
pclass - passenger class, (1=1st;
2=2nd;3=3rd); proxy for

socio-economic status (SES)
1st ~ Upper; 2nd ~ Middle; 3rd ~ Lower;

survived - survival (0=No; 1=Yes);

age - age (in years); fractional if age is less than 1;
sex -gender (female or male);

Question

What is the/a identifier variable? 

The Data is shown here
Variable Name      Description of Variable
name        -           full name of the passenger,
pclass         -                 passenger class, (1=1st;          
                                    2=2nd;3=3rd); proxy for  

                                    socio-economic status                      (SES) 
                1st ~ Upper; 2nd ~ Middle; 3rd ~ Lower;

survived            -            survival (0=No; 1=Yes);

age       -       age (in years); fractional if age is less than 1;
sex -gender (female or male);