Meta-analysis is a generic term applied to a collection of procedures leading to multiple study combinations. Not every meta-analysis is done the same way. Archie Cochrane developed a set of best practices to standardize the procedures so that all meta-analyses would or could follow the same (and stringent) protocol and the results from different meta-analyses can be compared.  

"The need for statistical synthesis methods to enable interpretation of results from multiple studies was recognized more than 50 years ago [1,75-77]. Meta-analyses now form a core component of many Cochrane Reviews. Without such a method, interpreting the effectiveness of an intervention is difficult, if not impossible. Further, metaanalysis allows the combining of results from a series of small studies, to answer a question regarding the effectiveness of an intervention, which could otherwise not be answered from the individual studies."

Read more in the attached paper file below "Meta-analysis and The Cochrane Collaboration: 20 years of the Cochrane Statistical Methods Group" by Joanne E McKenzie1, Georgia Salanti, Steff C Lewis and Douglas G Altman.