What is WOFF?
Not a typeface format but a wrapper: a TrueType or OpenType font compressed for the web, typically 40% smaller, and what @font-face expects. The outlines inside are untouched, so unwrapping one gives back exactly the font that went in.
What is OTF?
OpenType, which extends TrueType with cubic curves and the typographic machinery that makes real typesetting possible - ligatures, alternates, small caps, proper kerning. Where a typeface has ambitions, it usually ships as OTF.