As far as I know the term "bandwidth friendly" is not an official term, but a phrase I have invented. Just as something is "environmentally friendly" if it is not harmful to the environment, so "bandwidth friendly" applications do not harm the available bandwidth.
"Bandwidth" can very informally be regarded as a measure of the data carrying capacity of a data transmission system such as part of a network; so put crudely, a network link with a high bandwidth will deliver large amounts of data quickly, a low bandwidth link will take a long time to deliver small quantities of data.
A dial-up link over a Modem running at "28.8" or even an ISDN link has a much lower bandwidth than a Local Area Network running over 10Mbit Ethernet. For dial-up users it is particularly important to conserve bandwidth.
Cabletron Systems Ltd. produced a glossary of networking terms in which "bandwidth" is defined as: This is the range of signal frequencies that can be carried on a communications channel. The capacity of a channel is measured in cycles per second, or Hertz (Hz), between the highest and lowest frequencies. While this indicates the channel's information-bearing capacity, it is more commonly expressed as "bits per second". bandwidth varies according to the sort and method of transmission.