The technique used to categorize stakeholders according to their level of involvement in the project is the Power/Interest Grid. This technique is essential for identifying which stakeholders need to be managed closely and which can be monitored with less effort. The grid categorizes stakeholders based on their power to influence the project and their interest in the project's success. This categorization helps in devising appropriate stakeholder management strategies by assessing their power and interest levels and planning interactions accordingly.

References:

Business Analysis.pdf, "Stakeholder analysis...provides a means of categorising stakeholders in order to identify the most appropriate stakeholder management approach"​​.