Let's say you've a two playbooks, foo.yml and bar.yml. The include_tasks module can be used to include tasks from one playbook in another. For example, if foo.yml contains the following, then the tasks in foo.yml and bar.yml will be played.
- include_tasks: bar.yml
include_tasks must be used within tasks, like this.
- hosts: all tasks: - include_tasks: foo.yml
import_playbook cannot be run inside a task meaning that you would use import_playbook to run a play outside of tasks.