While bandwidth and speed aren't the same thing, they're closely related, which is why many people use the two terms interchangeably. The higher the bandwidth of service, the faster your connection speed will be on your devices. Both are measured in Megabits per second, or Mbps.
With high bandwidth, you can do more online activities at the same time, such as downloading music, browsing the internet, and streaming video in HD. A low-bandwidth connection, on the other hand, may lead to longer download and upload times, lower video quality, and buffering while streaming video or audio.