The term Passive House comes from Germany. It is not to be confused with passive solar heating or cooling, although that plays a part.

From the German Passiv Haus site:

A passive house is a building in which a comfortable interior climate can be maintained without active heating and cooling systems (Adamson 1987 and Feist 1988). The house heats and cools itself, hence “passive”.

For European passive construction, prerequisite to this capability is an annual heating requirement that is less than 15 kWh/(m²a) (4755 Btu/ft²/yr), not to be attained at the cost of an increase in use of energy for other purposes (e.g., electricity). Furthermore, the combined primary energy consumption of living area of a European passive house may not exceed 120 kWh/(m²a) (38039 Btu/ft²/yr) for heat, hot water and household electricity.

With this as a starting point, additional energy requirements may be completely covered using renewable energy sources.

This means that the combined energy consumption of a passive house is less than the average new European home requires for household electricity and hot water alone. The combined end energy consumed by a passive house is therefore less than a quarter of the energy consumed by the average new construction that complies with applicable national energy regulations.

Comparison of Energy Ratings of Homes
WSchVO = German Heat Protection Regulation
SBN = Swedish Construction Standard

A passive house is cost-effective when the combined capitalized costs (construction, including design and installed equipment, plus operating costs for 30 years) do not exceed those of an average new home.

Following are the basic features that distinguish passive house construction:

Compact form and good insulation: All components of the exterior shell of the house are insulated to achieve a U-factor that does not exceed 0.15 W/(m²K) (0.026 Btu/h/ft²/°F).
Southern orientation and shade considerations: Passive use of solar energy is a significant factor in passive house design.
Energy-efficient window glazing and frames: Windows (glazing and frames, combined) should have U-factors not exceeding 0.80 W/(m²K) (0.14 Btu/h/ft²/°F), with solar heat-gain coefficients around 50%.
Building envelope air-tightness: Air leakage through unsealed joints must be less than 0.6 times the house volume per hour.
Passive preheating of fresh air: Fresh air may be brought into the house through underground ducts that exchange heat with the soil. This preheats fresh air to a temperature above 5°C (41°F), even on cold winter days.
Highly efficient heat recovery from exhaust air
using an air-to-air heat exchanger:
Most of the perceptible heat in the exhaust air is transferred to the incoming fresh air (heat recovery rate over 80%).
Hot water supply using regenerative energy
Solar collectors or heat pumps provide energy for hot water.
Energy-saving household appliances: Low energy refrigerators, stoves, freezers, lamps, washers, dryers, etc. are indispensable in a passive house.