self

The self variable is present in all Objective-C methods. it is one of two hidden arguments passed to code that implements a method. The initial value of self is always the object that received the message that led to the method's execution.

The other hidden argument is _cmd, which identifies the message received.

The self and _cmd variables are described in Apple's document at /Developer/Documentation/Cocoa/OjectiveC/ObjC.pdf.