Pool

A Pool is a container of a single Process (contains the sequence flows between activities).

A Process is fully contained within the Pool. There is always at least one Pool.

Lane

Is a sub-partition within the Process. Lanes are used to differentiate elements as internal roles, position, department, etc. They represent functional areas that may be responsible for tasks.

Milestone

Is a sub-partition within the Process. It can indicate different stages during the Process.