The simple explanation

When you do anything online, whether that’s sending a WhatsApp message, joining a Zoom call, or loading a website, your data doesn’t travel as one big chunk. It gets broken up into tiny pieces called packets. Think of it like sending a long letter, but instead of posting it as one envelope, you split it into 100 numbered postcards and send them separately. The receiving end then puts them back in order to read the full message.

Packet loss is what happens when some of those postcards never arrive. They get dropped, delayed beyond use, or lost somewhere along the route between your device and the server you’re talking to. The receiving end is left with gaps, and depending on the type of data, it either has to ask for the missing pieces again or carry on without them.

What this looks like in real life

You’ve already experienced packet loss even if you didn’t know what to call it. It’s the video call where someone’s face freezes mid-sentence. It’s the online game where your character suddenly teleports backwards. It’s the Spotify track that stutters for a second, or the web page that hangs at 90% loaded. Those moments are usually packets that didn’t make it to your device in time.

Packet loss is measured as a percentage. If your computer sends 100 packets and only 97 come back, you’ve got 3% packet loss. Anything above 1% starts to be noticeable on real-time services like calls and gaming. Anything above 2% becomes genuinely frustrating. A healthy connection should sit at 0% most of the time, with occasional tiny blips that nobody would feel.

The technical layer

Under the hood, the protocol you’re using decides how the loss is handled. TCP, which runs most web traffic, file transfers, and email, will detect missing packets and ask the sender to resend them. That’s why a slow web page eventually loads. The data gets there, just later than it should. UDP, which runs voice calls, video, and most online games, doesn’t bother resending. By the time the packet would arrive, the moment has passed, so it just carries on with whatever data made it through. That’s why packet loss hits live services so much harder than it hits browsing.