If you've ever separated a mixture of compounds using column chromatography, you know how long and tedious the process can be. Also, recoveries are often fairly mediocre, due to severe tailing of each component as it slowly passes through the column.
In Flash Chromatography (a term coined by the developer of the method, Prof. W. Clark Still of Columbia Univ.), which is essentially a combination of column and medium-pressure techniques, compressed air or nitrogen is used to push the eluant through the column.1 Fractions are collected quickly, and the total time for a flash separation is under 15 minutes! The only true requirement is that the two analytes' Rf values be separated by at least 0.3 (+/- 0.1, depending on your experience and level of skill).
As with many techniques, the best thing is for you to read the original paper describing the technique, then to try it out under the watchful eye of someone who is experienced with the method.
1Still, W.C.; Khan, M.; Mitra, A. J. Org. Chem. 1978, 43, 2923; to see the actual paper, click here. For paper to open in a new window (makes printing easier), click here.