As a variable:
returnType (^blockName)(parameterTypes) = ^returnType(parameters) {...};
As a property:
@property (nonatomic, copy) returnType (^blockName)(parameterTypes);
As a method parameter:
- (void)methodWithBlock:(returnType (^)(parameterTypes))blockName;
As a typedef:
typedef returnType (^TypeName)(parameterTypes);
TypeName blockName = ^returnType(parameters) {...};