A cordless phone is a landline in which the base unit and the handset are linked by radio rather than by a cord. Because the handset travels with you, you can answer from anywhere in the house and keep talking as you move. Cordless models began spreading in Japan in the late 1980s, and by the 2020s a home telephone sold there normally comes with at least one cordless handset.
The earliest cordless phones were analogue. Call quality was poor, neighbouring sets interfered with one another, and there was a real risk of eavesdropping - that was the era when an off-the-shelf radio receiver could pick up someone else's conversation. Digital designs followed, and Japanese-market sets settled on digital cordless telephony in the 1.9 GHz band (the DECT method). Japan's Ministry of Internal Affairs and Communications classes these as radio stations that require no licence, and because calls are encrypted, interception has become far harder. The 1.9 GHz band also sits clear of the 2.4 GHz band used by Wi-Fi, so the clashes with wireless networks and microwave ovens that plagued the earlier 2.4 GHz generation no longer arise. Expect a working range of roughly 50m indoors and up to about 300m outdoors with clear line of sight, though reinforced concrete walls and different floors cut that sharply.
Cordless phones changed how people telephone. There was no longer any need to sit beside a phone on the wall: you could talk from the living room, the bedroom, or the kitchen. That experience of carrying a phone around arguably softened the ground for mobile phones and made them easier to accept.
Typical features include Number Display support, nuisance-call handling (a warning that tells the caller the conversation is being recorded, plus block lists), answering machine functions, and intercom calls between handsets. One point is easy to miss: showing the caller's number on screen takes more than a compatible handset - it requires a separate paid subscription from the telephone company. When someone buys a new phone and the number still fails to appear, that missing subscription is almost always why.
There is one weakness that matters in an emergency. A handset depends on power at the base unit, so during a blackout the handsets are simply dead. Even on models advertised as working through a power cut, what still works is normally only the corded receiver on the base unit itself. That, in turn, assumes an analogue subscriber line, which is fed with power from the telephone network; on a fibre-based IP phone the network-side equipment needs mains power too, so a blackout takes the line down altogether. If you are counting on a landline as your fallback when the power fails, check both of those points first. Note as well that handset batteries degrade over a few years: a handset that runs flat almost immediately usually needs a new rechargeable pack rather than a new phone, so choosing a model with replacement batteries still available will keep it usable for longer. Our history of the telephone as a device traces how landlines evolved.