Dr. Deming used to using the term continual improvement (rather than continuous improvement) later in his life because that would include continuous and dis-continuous improvement (innovation, etc.). I use continual improvement for that reason also. I think the improvement process

• must be never ending
• must focus daily on how any process can be improved
• must focus on adopting improvement systemically (not just locally, by one person or team)
• must focus on discontinuous improvement which could include high energy kaizen events and dramatic innovation
• must include a study phase (PDSA) where the improvements are evaluated to determine whether they actually had the anticipate effect
• and must include improvement of the improvement process itself

To me, continual improvement encompasses both continuous and discontinuous improvement.

Reflecting on: Continuous Improvement vs. Continual Improvement

Related: Process Improvement and Innovation - Better and Different - Kaizen the Toyota Way - Change is not Improvement - Think Long Term Act Daily - Encourage Improvement Action by Everyone