ad hoc basis

基本解释

Other plug-ins, such as the XM plug-in, are more specific and are installed by the user on an ad hoc basis.
另一些插件，如 XM 插件，具有更强的专用性，则由用户在需要的时候安装。
You can use a collaboration scope when you are creating a flow that will be modified on an ad-hoc basis, rather than having a highly structured flow.
在创建将在特别的基础上修改的流时，您可以使用协作范围而不是使用高度结构化的流。
For even more flexibility, you can replace or augment widgets' default classnames on an ad-hoc basis by calling their setStyleName() and addStyleName() methods.
要得到更多的灵活性，则可以调用小部件的 setStyleName() 和 addStyleName() 方法，临时替换和增加小部件的默认类名。

Afterward it ran evacuations for Forbes 500 companies and governments on an ad hoc basis.
FORBES: Flight To Safety
Review of systems access procedures, for example, moved from an ad hoc basis to every 90 days.
FORBES: Security
Like most railroads, Norfolk Southern used to run on an ad hoc basis--a train would leave the yard when it was ready.
FORBES: Magazine Article