Another definition: a consultant is someone who, when asked what time it is, will ask to borrow your watch. You should realize, however, that this is a valuable service if the client is blind.
[Disclaimer: I've been a consultant my entire professional life.]
My service is usually to remind them they have a watch, how to read it, when to read it and when to ignore it and why. Sometimes have to lead them to where their reading glasses were left. Consulting boils down to telling them something they really already know somewhere in deep bowels of their business.
KPI's to the rescue!