The Ford 351W-CP isn't a standard designation you'll find in official Ford literature. The "351W" refers to the popular 351 cubic inch Windsor small-block V8 engine. The "-CP" is likely a custom or aftermarket designation. It could refer to a specific build, modification, or perhaps a particular company's internal code for a crate engine or rebuilt unit.
Without more context (where you saw this designation, what the source said about it, etc.), it's impossible to say exactly what a "351W-CP" engine entails. It's a 351 Windsor, but the "CP" adds an unknown element.
