Compression is the process of reducing the size of data so it can be transferred, stored, or processed more efficiently. In web traffic, it often appears as HTTP content encoding, proxy-based rewriting, or compressed archives sent to save bandwidth and speed up delivery. For a self-hosted proxy, compression can make heavy pages lighter and faster to load.
In security work, compression matters because it changes how data moves through a system. Defenders use it to reduce network load and remove unnecessary bulk, but intermediaries that compress or decompress content must be trusted and configured carefully. Attackers can abuse compression to hide payloads, frustrate inspection, or trigger decompression bombs that expand into huge amounts of data and consume resources. Understanding where compression happens helps analysts spot both performance optimizations and potential abuse.