A landline phone is a phone line directly connected to the phone network. With today’s internet technology, some phone lines do not directly connect to the phone network; rather, they connect via the Internet.
A regular corded phone is a landline. So is a cordless phone that connects to the same phone jack as a regular corded phone.
Smartphones do not use landlines – they are a wireless device.
VoIP (Voice over IP) phones also do not use landlines – they carry phone signals over the internet.
Some phone providers put landline-style phone lines in that are based on a VoIP (Internet) protocol. They look and feel like landline phone lines. However, they may have the same incompatibilities with systems like fax that VoIP phones have.
Fax machines prefer landline phone lines. They are the best way to connect a fax machine to the phone network.