Answer:
The term "Linux" is used to describe both the kernel created by Linus Torvalds itself, as well as the group of operating systems that incorporate the kernel as part of a complete system. The intended definition depends on the context in which it is used. Different examples include:
1. I compiled Linux today.
This probably refers to compiling the kernel from source. Depending on the intention of the system, compiling everything a typical person would use could take up to a couple days.
2. I installed Linux today.
Most Linux distributions take less than an hour to install, making an installation in one day quite possible. Installing a kernel by itself would also be of little use to anyone, so it is most likely that someone is referring to the complete system in this context.
3. Would you like to try Linux?
This also refers to a complete system. Again, using just the Linux kernel without accompanying software doesn't get you very far.
4. Linux runs on many architectures, including x86, x86-64, PowerPC, ARM, and MIPS.
This refers to both complete systems and the kernel itself. However, it is a property of the kernel itself that allows this to happen, and certainly not all Linux distributions run on all architectures.