eField Trips are a way to visit sites and view the video they provide online. Many of the sites referenced under "What can I video conference about" also provide streamed video. One primary advantage of using one-way streaming is that you are in control of when to view and to how much time to spend. The primary disadvantage is that the efield trip/virtual visit is not interactive.
Unfortunately, there is no standarization among the terms efield trip, virtual visit, video conference, etc. An Internet search will produce a mixture.