Bandwidth is as it sounds - the width or capacity of the ‘pipe’ through which data transfers in and out of the Internet. Business Internet Service Providers (ISPs) own high-capacity connections to the Internet provisioned across different technologies. The ISP then rents out little ‘pipes’ of that connection to business subscribers. When a customer interacts with a cloud based application like Salesforce or Netsuite, or makes a phone call over a cloud based phone system like VoIP Phone System (Hosted PBX) - the data travels very quickly from wherever it is stored - across that bandwidth pipe rented to you by your ISP - to your computer, tablet or phone and back. The speed at which that data arrives at its destination depends on available bandwidth. If we think of the Internet as a giant tank of water, imagine the difference between draining it with a narrow hose or a big fat pipe. The fat pipe is wider, has more band-width than the narrow hose, so a lot more can flow through at one time.
Ultimately, all that is meant by the term bandwidth is how much data can pass through the pipe at a given time.