Magit buffers are organized into nested sections, which can be collapsed and expanded, similar to how sections are handled in Org mode. Each section also has a type, and some sections also have a value. For each section type there can also be a local keymap, shared by all sections of that type.
Taking advantage of the section value and type, many commands operate on the current section, or when the region is active and selects sections of the same type, all of the selected sections. Commands that only make sense for a particular section type (as opposed to just behaving differently depending on the type) are usually bound in section type keymaps.