What I say when someone asks what I do:

I work for a company called Undercurrent; we do strategy consulting for really big corporations. Our work generally falls into three big categories.
The first is product strategy; we help companies figure out what to build. Typically we're talking about digital products here, so it's along the lines of "we know we need a new website, but we don't really know what our website should *do.*"
The second is organizational design. Here our clients usually have a product that customers really want, but they're kinda bad at doing the work, so we help them figure out how to organize their team to be better.
The third is broader think-tank type stuff. There, we're brought in basically to be smart people who can provide an outside perspective on an industry or competitive landscape.