A formal expression meaning 'on the occasion of' or 'at the time of', used when referring to an event or action and often in announcements or instructions.
新学期にあたり、校長が全校集会で挨拶をした。
On the occasion of the new term, the principal gave a speech at the assembly.
開業にあたり、必要な書類をすべて提出してください。
When starting (a business), please submit all the required documents.
卒業式にあたり、学生代表がスピーチを行った。
At the graduation ceremony, the student representative gave a speech.