MVC Business Logic and Rule
ElYusubov’s answer mostly nails it, domain logic should go into the model and application logic into the controller.
Two clarifications:
The term business logic is rather useless here, because it is ambiguous. Business logic is an umbrella term for all logic that business-people care about, separating it from mere technicalities like how to store stuff in a database or how to render it on a screen. Both domain logic (“a valid email address looks like…") and workflows/business processes (“when a user signs up, ask for his/her email address") are considered business logic, with the former clearly belonging in the model and the latter being application logic that goes in the controller.
MVC is a pattern for putting stuff on a screen and allowing the user to interact with it, it does not specify storage at all. Most MVC-frameworks are full stack frameworks that go beyond mere MVC and do help you with storing your data, and because the data that should be stored are usually to be found in the model, these frameworks give you convenient ways of storing your model-data in a database, but that has nothing to do with MVC. Ideally, models should be persistence-agnostic and switching to a different type of storage should not affect model-code at all. Full fledged architectures have a persistence layer to handle this.
A1: Business Logic goes to Model part in MVC. Role of Model is to contain data and business logic. Controller on the other hand is responsible to receive user input and decide what to do.
A2: A Business Rule is part of Business Logic. They have a has a relationship. Business Logic has Business Rules.
Take a look at Wikipedia entry for MVC. Go to Overview where it mentions the flow of MVC pattern.
Also look at Wikipedia entry for Business Logic. It is mentioned that Business Logic is comprised of Business Rules and Workflow.