I had a look at the Kent Blogs site this afternoon, and one in particular rang bells with me: Ollie Double in the School of Arts talks about the need to keep it simple when writing up your research.
The same holds true for funding applications: the people assessing applications are rarely in exactly the same specialism as you, so you've got to talk to a general audience. The 'Summary' section, often overlooked as an afterthought, is key: it's your chance to get your foot in the door, to 'hook' the time-poor panel member, and explain, in simple terms, what your research question is, why it's important, how you're going to answer it, and how you're going to disseminate it effectively. Sounds obvious, but you'd be surprised how many people don't.
So avoid jargon if you can; there's usually easier ways to explain your research. Keep in mind Brecht's wooden donkey, mentioned in Ollie's blog, which apparently had a sign around its neck that said: 'even I must understand it'.