As the manual page of
lspci is a utility for displaying information about PCI buses in the system and devices connected to them.
So it lists all (PCI) devices connected to the PCI bus(es). Looking at a PCI id, e.g.
03:00.0 Network controller: Intel Corporation Wireless 7260 (rev 83), the
03:00.0 is the PCI bus slot (
Network controller part is the PCI slot class and the final text part is a description of the device.
Edit in response to the comment below:
According to The Debian Wiki,
lspci lists the PCI-like devices (AGP, PCI-Express, CardBus, Express Card, etc) that are connected to your computer. I guess it lists all devices directly connected to the north bridge, south bridge and, for more recent computers, the PCH.
Note that USB devices can be listed using
lsusb and CPU information via
lshw tool gives an even more detailed view of the hardware.