M – Model(Object, Fields, Relationships, Apex Classes)
V – View(Visualforce page, Pagelayouts, Record Types, Force.com Sites, Components)
C – Controller(Validation Rules, Controllers in a Visualforce page)
Model
- The database layer
- Contains objects, fields, and security
Controller
- The business logic layer
- Links the Model to the View
- Contains Workflow, Validation Rules, Apex
View
- The user interface layer
- Tabs, Page Layouts, Visual Force