1. (报纸、杂志的)发行量，销售量
    The circulation of a newspaper or magazine is the number of copies that are sold each time it is produced.

circulation的意思

    e.g. The Daily News once had the highest circulation of any daily in the country...
           《每日新闻报》的发行量曾位居全国所有日报之首。
    e.g. The paper has proved unable to maintain its circulation figures.
           事实证明这家报纸难以维持其发行量。

2. 血液循环
    Your circulation is the movement of blood through your body.

    e.g. Anyone with heart, lung or circulation problems should seek medical advice before flying.
           有心肺疾病或血液循环问题的人在乘坐飞机前应寻求医生建议。
    e.g. ...cold spots in the fingers caused by poor circulation.
           血液循环不畅导致的手指上的冻疮

3. see also: circulate

4. (货币等)流通/不流通/退出流通
    If something such as money is in circulation, it is being used by the public. If something is out of circulation or has been withdrawn from circulation, it is no longer available for use by the public.

    e.g. The supply of money in circulation was drastically reduced overnight.
           流通领域的货币供应量一夜骤减。
    e.g. ...a society like America, with perhaps 180 million guns in circulation.
           像美国这样一个约有1.8亿支枪流散在外的社会

5. (一段时间)不出现在公共场合，不参加社交活动;坐牢;服刑
    If someone is out of circulation, they do not appear in public or at social gatherings for a period of time. You can also say that someone is out of circulation when they are in prison.

    e.g. Political trials were being used to keep prominent activists out of circulation...
           通过对著名活动家进行政治审判使其从公众视线中消失。
    e.g. I had been out of circulation for a month and knew that many friends would be there.
           我有一个月深居简出，不过我知道许多朋友正等着我。