Meta-analysis takes the results of two or more studies of the same research question and combines them into a single analysis. The purpose of meta-analysis is to gain greater accuracy and statistical power by taking advantage of the large sample size resulting from the cumulation of results over multiple studies. Meta-analysis typically uses the summary statistics from the individual studies, without requiring access to the full data set. Key components of meta-analysis include ensuring the availability of a common metric (statistic) across all studies, and the use of appropriate algorithms for combining or averaging those metrics across studies and assessing statistical significance.
See also: http://www.mnsinc.com/solomon/MetaA/MApage2.html#LinksAnch