It’s a plain white cake type common in the USA, which has various other plain white baked products like (often awful) industrial white bread.
”What is the difference between white cake and vanilla cake?
The main difference between a white cake and a vanilla cake is that a white cake uses egg whites rather than whole eggs, as the yolks tint the batter yellow.”
- From the Classic White Cake page By Olivia on the “liv for cake” (sic) web site.
Oh, and if you despise the linguistic folly of “white cake”, you may also like the expression common in some parts of the USA (the east and/or south?) where it is said that a person might “eat some McDonald’s”. I.e. using the name of the restaurant (usually an industrial fast food chain) as the thing they are talking about eating, when they mean some “food” from such a restaurant brand name.