Can someone explain the acculmulation theory - I seem to have missed it and I'm stuck with the contrary opinion of financial definitions of "accumulation"?

Is accumulation the write word for what is going on - given it's financial definition (example below)?

Accumulation 
This is another way of saying: professional buying. A stock is under accumulation when volume expands on days when price moves up. 

http://www.marketwatch.com/pf/started/gettingstarted_glossary.asp