Is it a literal hood that's used to simulate IMC?
When you read or hear the term "under the hood" as it relates to simulated IMC, it may or may not be an actual hood. The FAA does not require a hood, instead the FAA calls for a "view limiting device." Often the view limiting device used is a hood such as the ones depicted below. However, other view limiting devices can also be used, such as glasses with an opaque coating that limits your view such as the ones depicted in the last picture below the hoods. 

Checkout this "superhood" at Sporty's!



This is the type I used for my IFR certificate back in the day.



This is another type of view limiting device that can be used to simulate IMC. It is commonly still referred to as "under the hood" or as "hood-word", but as you can see these are not a hood. There is a name brand of glasses like these called "foggles." And most people refer to these as "foggles", although, these, are a different brand.