Method access modifier ใน objective-c

‘-’ in the front of the definition, signifies that the method is an instance method.
‘+’ to define a class method (more on class methods in a future post).

credit : http://macdevelopertips.com/objective-c/objective-c-defining-a-class.html

ความหมายของ prefix "NS"

อ้างอิงจาก wiki ละกัน

NEXTSTEP, an object-oriented, multitasking operating system by NeXT, as well as a prefix for certain system-provided classes in the operating system, such as "NSString"

มันคือ nextstep นั้นเอง

http://en.wikipedia.org/wiki/NS