Throughout this guide, we define authorship. Some contributors may not meet the definition or criteria to be considered an author on a specific publication, but may still be deserving of acknowledgement in the final publication. When starting any project, discuss with your collaborators about expectations for authorship and acknowledgement.
The International Committee of Medical Journal Editors (ICMJE) provides the following list of examples of activities or contributions that only wouldn't constitute authorship but would constitute acknowledgement:
Some readers may see acknowledgement of an individual as their endorsement of your publication. As such, you should seek permission from any individuals who you plan to acknowledge. You shouldn't list anyone in your acknowledgements if they haven't been involved in the work or given their endorsements as their inclusion may be misleading for readers.
When acknowledging individuals, you may acknowledge them individually or collectively, and you should identify their specific contribution (e.g., reviewed an early draft of the manuscript).