1. In general, a broadcast describes a message or data sent to more than one person or device. For example, TV shows are broadcasted to all subscribers of a channel.
2. With networking, the broadcast address is used to distribute a signal across a network, commonly used for declaring devices and their information on a network. A broadcast address on a network is an address that ends with 255. For example, a broadcast Netmask is 255.255.255.255.
With network equipment one of the big differences between a network hub, switch, and router is that a hub broadcasts all packets across all ports on the hub. However, a network switch and router looks at each packet to determine its destination and only sends the information to the destination intended to receive the information.
3. With wireless networks, wireless routers broadcast the SSID, which allows all wireless devices to find wireless networks. Because wireless networks are usually set to broadcast their SSID you may see your neighbors wireless network when trying to find your own wireless network.