Sentence:  In the special case of the algebra \mathbf{D} of <WSD>dual numbers</WSD> we get the vertical tangent bundle V. 
Meaning of the word marked with <WSD> tags:  An element of an algebra (the "algebra of dual numbers") which includes the real numbers and an element &epsilon; which satisfies &epsilon; ≠ 0 and &epsilon;&sup2; = 0.