Accumulation is when there is still volume being poured into the stock but it isn't making significant moves either in the upside or downside. Usually though the stock tends to dip slowly downwards. Eventually the float will be taken up if the volume continues and eventually it takes little volume to significantly move the stock in either the upward direction or downward direction. This is due to the low supply (because of accumulation) and the same volume or higher volume being poured in.
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