Gathering metrics for your agile team will help them find opportunities for improvement in both the product and themselves.
Empirical process control is a technique used when the complexity of activities means a defined process control cannot be employed.
Incremental development slices work into small bite-sized pieces. These are called increments. Each increment builds on top of what has gone before. Fully functional modules grow bit-by-bit over time. Each evolution adds to preceding functionality.
Iterative development is the process of repeating and refining a cycle/way of working. This is called an iteration.