不常用软件的英语缩写是 NUI，它来源于 "not frequently used software" 的缩写。

例句：

NUI programs often require more resources and may be less stable than frequently used software.
NUI 程序通常需要更多的资源，可能比常用软件不稳定。
Many computer users have a lot of NUI on their devices that they don't even know they have installed.
许多电脑用户的设备上有很多 NUI，他们甚至不知道它们已经安装了。
Some NUI may have security vulnerabipties, so it's important to keep them updated or remove them if they're not needed.
一些 NUI 可能存在安全漏洞，因此重要的是保持更新或在不需要时删除它们。