In some papers there is "launch energy" characteristic of spacecraft launched into space from Earth. Sometimes it is written as "C₃" (C3). For example, Ares V document lists "C₃" as equal or less than 35 km²/s².
What is the meaning of "C₃" (Characteristic energy?), and what is difference between 35 km²/s² (start from Earth), 10 km²/s² ("delivering 8 tonn to mars at a C₃ of 10 km²/s²"), 80 km²/s² (required for sample return from Jovian moons), and 110 km²/s² (needed to reach Saturn without gravity assists - in direct mission)