A packet is a small, formatted block of data that is transmitted over a packet-switched network, like the internet or a local area network (LAN). When a large piece of data, such as a command string or a data file, needs to be sent across a network, it is first broken down into smaller, more manageable pieces. Each of these pieces is then wrapped in a "packet" which contains not only the data itself (the "payload") but also control information in the form of headers.
This header information is like the address and postage on an envelope; it contains crucial details needed to get the packet to its destination and reassemble it correctly. This typically includes the source and destination IP addresses, the source and destination port numbers, a sequence number indicating the packet's order in the original data stream, and error-checking information like a checksum. Routers and switches in the network use the header information to forward the packet along its path. At the receiving end, the device collects all the packets, uses the sequence numbers to put them back in the correct order, and reassembles the original data.
This packet-based approach is efficient and robust, as it allows multiple users to share the same network, and if one packet is lost or corrupted, only that small packet needs to be re-sent, not the entire data file.
The maximum packet size is determined by the MTU (Maximum Transmission Unit) and is limited to a maximum of 1,500.