The phrase "plain vanilla" means something that is basic, ordinary, or without any special features or qualities. It is used to describe something that is quite simple or plain in comparison to other options. Full definition
Same applies for plain vanilla ETFs that pass through the dividend to the investor. (canadiancapitalist.com)
This competition works to both drive down the expense ratio of plain vanilla funds at the same time generating new, more specialized funds with higher expense ratios. (abnormalreturns.com)
The sum total of these two effects is to drive down the cost of holding plain vanilla index funds down toward zero. (abnormalreturns.com)