The
principle that it can be
presumed that everyone is willing for their
organs to be used to save lives when they die, and that those who do not agree have to explicitly
opt out during their lifetime.
Many European countries already operate by presumed consent, and the opt-out rate is only about 2%.
Given the quite small proportion of people who go to the trouble of carrying an organ donor's card, this is a great improvement, and shows that most people are at worst indifferent about the matter.
"Soft" presumed consent is when relatives are consulted at the time of death in case any of them have any strong objections that would override the presumed consent.