Packet

A packet is a construct of bits or bytes that gets sent over LAN or WAN links in order to make the internet work. A packet holds the data used in telecommunication. A packet, also called a frame, has a header and a body (or payload). Inside the header there is a destination and a source address. Given that information a router knows where to send the packet and if it doesn't know it'll send a reply packet indicating the error (see Icmp).