Cold Crashing: Reducing the temperature of a finished beer for a relatively short amount of time, i.e. days, in order to get much of the suspended matter to drop out before packaging. Usually done in a primary fermenter.
Lagering = Cold Conditioning: Reducing the temperature of a finished beer for weeks or months, in order to get suspended matter to drop out and get a very clear beer, i.e. clearer than what can be obtained from just cold crashing . Usually done in a secondary vessel or serving keg. Technically, every beer that's stored cold for an extended period of time is being lagered.
Lagering is usually done with bottom fermenting yeast. Cold crashing is something you usually hear being done by those of us making ales and IPA's with top fermenting yeast. However I don't cold crash. I feel that I get better or at least just as good a result by waiting additional time for everything to drop out of suspension. Might take 3 days longer or might take 3 weeks longer. I'm not in a hurry.