16th death anniversary; 16th memorial service
Buddhist memorial service held on the 16th anniversary of a person's death. Part of a series of periodic memorials; the counting includes the first anniversary as 一周忌, so 十七回忌 is the 16th year after death.
Next month is the 16th memorial service for my grandmother.
The first anniversary memorial service, held one year after death. 十七回忌 is the 16th such service.
The second anniversary memorial service, held two years after death. 十七回忌 is a later service in the same series.
Compound of 十七 (seventeen) + 回忌 (anniversary of death). The term follows the Buddhist tradition of counting memorial services, where the first anniversary is called 一周忌, so the 17th service corresponds to the 16th year after death.