ETI refers to Extra Terrestrial Intelligence. For our purposes, we can consider "Life" to include any organisms brought forth via evolution by natural selection. More broadly, life may include creatures that do not evolve, as a creature that maintains metabolism and homeostasis and so on might very well be considered alive. It may also include non-natural, artificial, selection - artificial life. And it may include stranger forms of evolution, as for example a process by which a certain organism is always improved and changed rather than breeding and competing with its descendants. However, let us limit ourselves to an understanding of life as the arisal of evolutionary processes against the background of a lifeless natural universe.