This can be literal (as in a rope thrown to a drowning or stranded swimmer to pull him onto a boat), or figurative (calling a social worker who contacts elderly residents living alone a "lifeline to support services").
Random House Abridge Dictionary, def. 8: Assistance at a critical time.
I am giving one example from an article found online, with a rough translation. I tried to pick an example that was not political -- apparently a church program for couples who are having marital problems.
As an aside, I also saw "slamka spasa" in contexts where it might be translated as "last resort," but it does not work in every instance.

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Note added at 6 days (2011-03-02 18:04:24 GMT)
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Random House Abridged (typo -- left out the D)