Plain English is English written to be readable and concise to the broadest segment of a population. Or ... English that is easily understood.
Chrissie Maher founded Britain's first community newspaper in 1971, intended to be written in a common, colloquial style. In 1974, while helping ordinary people claim social security benefits from the government, she was concerned that the English used in application forms provided by the government was needlessly complicated. So, for five years Chrissie unsuccessfully lobbied the British government to simplify the language it uses in its communication with the public. Ultimately she managed to attact some attention when dressed the Gobbledygook Monster she delivered the first tracts of the Plain English Magazine to 10 Downing Street. In 1981 the government launched an inquiry headed by Sir Derek Rayner to investigate poorly written English, and in 1984 the guide The word is Plain English was distributed to British public servants.
Chrissie set up Plain English Campaign, which runs training programmes for writers, and brands the Crystal Mark logo to endorse clearly written text. Notorious cases are also distinguished with the Golden Bull award : the National Health Service won the award in 1993 when it required 229 words to define what a bed is :
A bed is a device or arrangement that may be used to permit a patient to lie down when the need to do so is a consequence of the patient's condition rather than a need for active intervention such as examination, diagnostic investigation, manipulative treatment, obstetric delivery or transport.
Beds, couches, or trolleys are also counted as hospital beds where:
a) used regularly to permit a patient to lie down rather than for merely examination or transport (e.g. in a day surgery ward.)
b) used whilst attending for a specific short procedure taking an hour or less such as endoscopy, provided that such devices are used only because of the active intervention and not because of the patient's condition.
c) used regularly as a means of support for patients needing a lengthy procedure such as renal dialysis (includes special chairs etc.)
d) used regularly to allow patients to lie down after sedation.
NB: A device specifically and solely for the purpose of delivery should not be counted as a bed.'
A good passage (I mean 'A good example') of plain English would use medium sized sentences, active voice, everyday English vocabulary to describe concise meanings, simple sentence structures and the use of headings and typefaces that help present ideas in a clear logical order. Plain English avoids words that are vague, jargon or wanky.
There is no reason to deliberately create a linguistic barrier between yourself and your audience. Plain English is a useful skill - not just for writing government correspondence, but also in compiling Everything2 entries too.