There is none. manufactures over the years have debated what to call this light. I personally prefer "check engine" to service engine soon" which implies some kind of maintenance service is due. Most schools and government agencies dealing with auto repair now call these lights MIL (malfunction indicator light) which is some what better than the other two. MIL lights also include a yellow warning light the shape of and engine with no words. In the real world all yellow warning lights which turn on when there is a fault detected by the power train control module(s) are generically called "check engine" lights as that was the first term introduced into the industry.
There is a BIG difference between the two lights. The Check engine light is when something is wrong with one of the functions of your car end can be diagnoised with a OB2 scanner to tellthe problem!! The Service Engine soon light comes on when there is nothing wrong with your car it just comes on every 3000 miles or so. That is because they want you to bring it in to change the oil. Like the light to change your filter in your frig!!!