1. 电话接线员
    An operator is a person who connects telephone calls at a telephone exchange or in a place such as an office or hotel.

    e.g. He dialled the operator and put in a call for Rome.
           他拨了接线员的号，让他接通一个到罗马的电话。

2. （机器）操作员，技工
    An operator is a person who is employed to operate or control a machine.

    e.g. ...computer operators.
           计算机操作员

3. （企业的）经营者；运营公司
    An operator is a person or a company that runs a business.

    e.g. ...'Tele-Communications', the nation's largest cable TV operator.
           全国最大的有线电视运营商“电视通信公司”

4. 精明圆滑的人；善于取巧的人
    If you call someone a good operator, you mean that they are skilful at achieving what they want, often in a slightly dishonest way.

    e.g. He was a smart operator. Don't underestimate him.
           他这个人精明圆滑，可别小瞧了他。
    e.g. ...one of the shrewdest political operators in the Arab World.
           阿拉伯世界最精明狡猾的政客之一

5. see also: tour operator