KVC stands for Key-Value-Coding. It refers to accessing a property or value using a string.
id someValue = [myObject valueForKeyPath:@”foo.bar.baz”];
Which could be the same as:
id someValue = [[[myObject foo] bar] baz];

KOC stands for Key-Value-Observing. It allows programmers to observe changes in property or value.
In order to observe a property using KVO, you should identify the property with a string. The observable object must be KVC compliant.
[myObject addObserver:self forKeyPath:@”foo.bar.baz” options:0 context:NULL];

BY Best Interview Question ON 13 Jan 2019