volunteer activity
释义：在留学文书里怎么表示“志愿活动”呢？事实上volunteer可以作为形容词，表明“志愿者”相关的事物。相对的，voluntary的含义会更宽泛一些，有“自主、自发”的意思，比较容易令人误会。
例句：
The findings demonstrate a statistically significant relationship between years of experience in the social services field and number of hours of volunteer activity per month; as years of experience increased, so too did the amount of time devoted to volunteer activities.