A consultant will make sure that both sides (business and IT) will come to a common understanding - he speaks the language of both these worlds.
A consultant interconnects business and IT specialists because he is both an IT professional and a good communicator.
Specialist for a specific area or technology (to an extent). Suggests solutions alternatives for the cutomer. Expert at collecting requirements. Takes part in customer communication (as opposed to a specialist who doesn't). A consultant translates issues from business to technical language and vice versa.
Solution designs, facilitates communication among all parties involved
Good soft skills - has to communicate well with the client. Has an understanding of his/her technical area of expertise.
Business analyst, specialist, project manager, both enterprise & system architects.