A specific learning difficulty often affects the learning of specific skills so dyslexia is associated with the use of words (viz., reading them, spelling them, and - by extension with organising and producing written material). Dyspraxia, on the other hand, is a specific learning difficulty that affects learning gross or fine motor movement (including the movement of the speech organs).

Some (people) are affected by specific learning difficulties that do not have special names; we all know (people) who seem bright in many areas, but whose learning of some things is disrupted by very poor memory, chaotic attention control, or subtly disorganised interpretation or use of language.” (3)

SPELD NSW, a charitable organisation in NSW offers this useful profile of SpLD on the home page of its website. (4) SpLDs:
• are intrinsic to the individual
• are not linked to intellectual impairment (except incidentally)
• may coincidentally exist with problems in self-regulatory behaviours, social perception and social interaction
• are life-long
• result in difficulty being successful at school unless identified early and appropriate educational adjustments are provided to prevent failure.

References:
(3) http://search.ngfl.gov.uk/senco-forum//senco-forum.archive.1998/msg00700.html
(4) www.users.bigpond.com/speldnsw