A packet analyzer is a software program or computer hardware (packet capture appliance) that is used to catch and then log traffic traversing a computer network or part of that network. A packet analyzer may also be referred to as a network analyzer, packet sniffer, or protocol analyzer. (The terms  network analyzer and protocol analyzer can also have other meanings.)
Packet capture occurs when the analyzer intercepts each packet as the data streams flow throughout the network. In some cases, the analyzer is tasked with decoding raw data found in the packet in order to reveal the values of certain fields found in the packet. The contents of the packet are analyzed per the applicable specifications.
When a packet analyzer is employed to capture traffic on a wireless network, it is referred to as a wireless analyzer.