stands for Survival, Evasion, Resistance, and Escape.  The words are in that order as those are the phases.

First, if you are a pilot and are shot down, the first thing you need to do is survive off of the land.  If you are in bad guy territory, then you need to evade those searching for you.  If you are caught, then you need to resist as best you can and finally, if the opportunity ever presents itself, you need to escape.

The resistance phase of training is to innoculate one, to introduce at a minimum level of intensity and duration, what may be done to you in captivity.  But still an intense program any way.  This is horribly ironic that the methods used in training in a mock POW camp came from not only historical records but from Vietnam and Korean era POWs themselves.  Treatment considered horrible, immoral, and illegal.

Now we, the US, are the ones employing such techniques

"Schiller sprach zu Goethe, Steck in dem Arsch die Flöte! Goethe sagte zu Schiller, Mein Arsch ist kein Triller!"