For CMake's "install" command, what can the COMPONENT argument do?

I don't know what the argument COMPONENT of the install() command means, and I don't understand the CMake documentation for this. What is it in more detail?

What would an example be?

You can group installation targets into components, for example, "docs", "libs", "runtime", etc.

add_library(libone libone.c)
add_executable(one main1.c)
install(TARGETS libone one DESTINATION /somedir COMPONENT comp_one)

add_library(libtwo libtwo.c)
add_executable(two main2.c)
install(TARGETS libtwo two DESTINATION /somedir COMPONENT comp_two)

This makes it possible to run cmake -DCOMPONENT=comp_one -P {your_build_dir}/cmake_install.cmake to install only the libone library and the one executable. When you issue make install all components are installed.