an access point
An access point is the central radio that your Wi-Fi devices talk to — the hub of the conversation. Picture a receptionist at a desk: everyone in the room speaks to the receptionist rather than shouting across to each other, and the receptionist passes messages on to the rest of the building. The access point plays that role. Wireless devices send their frames to the AP, and the AP forwards them onto the wired network (and onward to the Internet) and relays incoming frames back to the right device.
Concretely, an access point bridges the wireless world and the wired world at the link layer. On the radio side it advertises a network name (the SSID), accepts devices through association, and runs the CSMA/CA medium-access rules and acknowledgments. On the wired side it typically connects by Ethernet cable to a switch or, in a home, sits inside the same box as the router and modem. The AP and the devices currently associated with it form a basic service set; bigger spaces use many APs sharing one SSID so you can roam between them. Note the common confusion: a home Wi-Fi router is several devices in one enclosure — a router, a switch, and an access point — and only the AP part is doing Wi-Fi.
Why it matters: the AP is where the air meets the wire, so its placement, channel choice, and load shape how good your Wi-Fi feels. Every device in range shares the AP's air time, so one busy AP can feel slow even with a strong signal. And because all your wireless traffic flows through the AP, it is also a natural place for security: it enforces the WPA password and encrypts the radio link, but, as always, that protects only the hop to the AP, not the whole Internet path.
A coffee shop puts three access points across the ceiling, all broadcasting the SSID CafeFree. As you carry your laptop from the window to the back, your device hands off from one AP to the next without you noticing — same network name, different radio doing the work.
Many APs, one SSID: roam without changing networks.
An access point operates at layer 2 like a bridge; it does not by itself assign IP addresses or route to the Internet. In a home router those jobs (DHCP, routing, NAT) are done by other parts of the same box, not by the AP.