From Style in Guide part of ABC of Plain Words by Sir E Gowers (1951)

A dictionary definition of jargon is

"a word applied contemptuously to the language of scholars, the terminology of a science or art, or the cant of a class, sect, trade, or profession".Perrin, Writer's Guide

When it was confined to that sense it was a useful word. But it has been handled so promiscuously of recent years that the edge has been taken off it, and now, as has been well said, it signifies little more than any speech that a person feels to be inferior to his own.

When officials are accused of writing jargon, what is usually meant is that they affect a pompous and flabby verbosity. The Americans have a pleasant word for it —"gobbledygook". It cannot be questioned that there is too much of that sort of thing in the general run of present-day writing, both official and other. Why this should be so, and how it can be cured, is one of the purposes of this book to examine. See for instance Abstract Words, Explanation, Gobbledygook, Position.

But there is also a jargon in the strict sense of the word, and official writing is not free from it. Technical terms are used — especially conventional phrases invented by a government department — which are understood inside the department but are unintelligible to outsiders. That is true jargon. A circular from the headquarters of a department to its regional officers begins:

The physical progressing of building cases should be confined to...

Nobody could say what meaning this was intended to convey unless he held the key. It is not English, except in the sense that the words are English words. They are a group of symbols used in conventional senses known only to the parties to the convention. It may be said that no harm is done, because the instruction is not meant to be read by anyone unfamiliar with the departmental jargon. But using jargon is a dangerous habit; it is easy to forget that the public do not understand it, and to slip into the use of it in explaining things to them. If that is done, those seeking enlightenment will find themselves plunged in even deeper obscurity.

Let us take another example. "Distribution of industry policy" is an expression well understood in the Board of Trade and other departments concerned with the subject. But it is jargon. Intrinsically the phrase has no certain meaning. Not even its grammatical construction is clear. So far as the words go, it is at least as likely that it refers to distributing something called "industry-policy" as to a policy of distributing industry. Even when we know that "distribution-of-industry" is a compound noun-adjective qualifying [policy], we still do not give to the words the full meaning that those who invented the phrase intended it to have. The esoteric meaning attached to this clump of ungrammatical nonsense is the policy of exercising governmental control over the establishment of new factories in such a way as to minimise the risk of local mass unemployment. No doubt it is convenient to have a label for anything that can only be explained so cumbrously. But it must not be forgotten that what is written on the label consists of code symbols unintelligible to the outsider. If the initiated want to communicate with those who are outside their mysteries, they must use language that everyone understands.