0Grapher: I'm sure that most people who aren't Linux experts mean more than a kernel when talking about an OS.
That's why you shouldn't call Linus Torvalds the creator of Linux but call him the creator of the Linux Kernel.
I usually refer to kernel as Linux, unless obvious from the context or specifically emphasised that OS is being discussed (like in "Which OS are you using? Linux."), but for the sake of total clarity especially aimed at newcomers, your comment is duly noted.
Although RMS would have something to add, probably that there is no ambiguity. When you say Linux, that's the kernel part, and if you want to address the OS, use GNU/Linux. This is known to stir endless debates which is not my intention, just adding more info for completeness.