Accumulation

Think about it like leaves in a rain gutter. Only they're made of gold. Or at least cash cabbage greenbacks.

Institutional investors wanting to own a huge, say, 15% stake in a large company accumulate shares over many trading days. Insurance/annuity buyers accumulate units of ownership in that policy over time. Investors wanting to live on the throw from dividends and bonds, such that they match what they earn in a normal working year...i.e. so that they can retire in style...accumulate that stream of dividends and interest payments over time.

Yeah, accumulation is all about collecting over time. Like those leaves in the gutter, which will probably sit there until you have children who you can order to do your chores for you.