What is standard vga graphics adapter?

It's the adapter that connects to a DVI-I output on a graphics card or motherboard.

DVI-I ("I" for integrated) has pins for BOTH the digital outputs and analog (VGA) outputs. The VGA adapter simply connects only to the analog pins.

DVI-D looks similar but only has digital pins so you can't connect a VGA adapter to one of those:
http://en.wikipedia.org/wiki/Digital_Visual_Interface#Connector

*I assume the "Standard" part of your title refers to the item I'm talking about instead of other similar adapters.