Broadband is having no generally accepted definition as each service, company or person defines it differently. Here are few examples:
“Broadband is a transmission capacity that is faster than primary rate ISDN, at 1.5-2 Mbit/s”
–International Telecommunication Union
“Broadband is a technology providing downstream speed in excess of 256 Kb/s”
-OECD
“Broadband is a connection of at least 200 Kb/s in one direction”
-US Federal Communications Commission
From all these statements we could summarize following definition:
“Broadband is a high-speed Internet connectivity service with the potential to always be connected. Definition of the ‘high-speed’ must be based on location capabilities”
–AD-net technology Co., ltd
Definition may vary depending on person, who is asked and country to which person belongs. Anyway, considering trends for FTTH and IPTV, especially HD channels delivered over IP, anything less of 2 Mbit/s is hardly to be considered as broad band.
By the way, you can find various service bandwidth requirements here: https://www.ad-net.com.tw/index.php?id=782