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.
Are they landlines? The gray area
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.