packet
also: datagram, frame
A packet is a small unit of data transmitted over a network, containing the actual information plus header information like source and destination addresses.
A packet is the fundamental unit of data sent across networks. It consists of a header (containing metadata like source IP, destination IP, and protocol type) and a payload (the actual data being transmitted).
Think of a packet like a postcard: the addresses and routing information are the header, while the message written on the card is the payload. When you download a file or browse a website, your data is broken into many packets, sent individually across the internet, and reassembled at the destination.
Different network layers use different packet names—frames at the link layer, packets at the network layer (IP), and segments at the transport layer (TCP/UDP). Network tools like tcpdump and wireshark capture and analyze packets to troubleshoot connectivity issues.