attr_accessor and attr_accessible in Rails

While trying to figure out why I was getting this error in a Rails application:

 WARNING: Can't mass-assign protected attributes  

I realised I'd confused the two below terms in my Rails model:

 attr_accessor  

is built into Ruby and defines a getter and setter method for a class attribute.

 attr_accessible  

is defined by Rails and makes the attribute mass-assignable.

Generally, in a Rails application, it's attr_accessible we want to be using.