High-speed bandwidth means your VPS is connected to a network port at a specified speed (for example, 1 Gbps) and you can use that port to its full capacity 24/7 without any traffic limits. There are no monthly transfer caps, no per-gigabyte charges, and no throttling when you hit some invisible threshold.
This is fundamentally different from plans that advertise large transfer allowances. A plan with 10TB of bandwidth sounds generous, but a busy streaming server or high-traffic website can burn through that in days. With high-speed bandwidth, you simply use what you need without watching a counter tick down.