Land based.  Landline refers to telephone company cables buried in the ground or strung on poles throughout the neighborhood.  Contrast with wireless communications such as Wi-Fi, cellular and satellite.  A desk phone is a landline if it is plugged into a telephone company wall outlet.  A desk phone wired to the Internet is called an "IP phone" and is not considered a landline (see 
IP phone).
No More Copper By 2029?
In 2024, AT&T announced that it would eliminate all landline service by 2029.  The copper wire infrastructure, around for decades, is costly to repair.  However, there has already been a loud outcry from rural areas as well as senior citizens who have no cellphones or Internet service.  Stay tuned!  See 
telephone.