What it is
Normally an IP address lives in one place. With anycast, the same address is announced from many locations, and internet routing delivers each client to whichever announcement is closest in network terms. Nobody chooses; the routing table does. The result is shorter paths for legitimate users, without any DNS or client-side logic.
Why it matters for Minecraft
Two reasons. Latency: a player in Warsaw and a player in São Paulo hit different entry points for the same hostname, so protection stops meaning a detour. Absorption: an attacker aiming a flood at one address finds it divided across every site announcing it, so no single location has to absorb the whole thing. This is why capacity figures for anycast networks are quoted as a total across the fabric.
What it does not do
Anycast is a routing property, not a filter. It gets traffic to a good place and splits volume; it has no opinion about whether the traffic is a player or a bot. Everything above the packet layer still has to be decided by something that reads the protocol.
Common questions
Does anycast add latency to Minecraft?+
Usually it removes some. Players connect to the nearest entry point rather than crossing an ocean to reach your host directly, so for a geographically spread player base the filtered path is often shorter than the direct one would have been.
Is anycast the same as a CDN?+
Related but not the same. CDNs commonly use anycast to route users to nearby caches, but anycast itself is just the addressing and routing behaviour. For a game protocol there is nothing to cache — the value is routing and absorption, not content delivery.