A systematic review that uses quantitative methods to summarize the results.
A meta-analysis is when all the information from a number of different (but similar) studies is pooled. It should not be about adding small piles of rubbish together to make a big pile of rubbish. It is only worth doing when individual trials are themselves of sufficient quality and validity. What meta-analysis does is to give enough size to have the power to see the result clearly, without the noise of the random play of chance.
Any meta-analysis must have enough events to make sense. Combining small, poor, trials, with few events will mislead.