From BusinessDictionary.com: Formal procedure by which an accredited or authorized person or agency assesses and verifies (and attests in writing by issuing a certificate) the attributes, characteristics, quality, qualification, or status of individuals or organizations, goods or services, procedures or processes, or events or situations, in accordance with established requirements or standards.
The Certification program for Certified Inventory Specialists, created jointly with the Inventory Institute, refers to the confirmation that you have completed the stated requirements. The association management standards are to confirm this accomplishment through either an external review, assessment, or education. This standard is met through the achievement of a stated number of CEUs along with passing the specified courses and the Certification Exam.
This is simply the letters you use after your name to indicate that you have successfully completed your certification. Doctors add MD and PhD after their name; nurses include RN, accountants proudly include CPA; the inventory professional earns the letters CIS, stating that they are a Certified Inventory Specialist.
So, in a nutshell, you use your designation letters (CIS) to tell your prospects, clients, other professionals, and fellow industry members that you have taken a leadership role and have achieved your certification, that you have achieved the designation of being a Certified Inventory Specialist.