The most basic definition of Anglish is English without words borrowed from other languages.
But beyond this definition, there is a wide range of personal interpretations of what constitutes Anglish. Some may only wish to write making the best of English words available, avoiding borrowed where possible, but accepting them where necessary. Other may wish to remove all borrowed words, and where there is no existing alternative in English, to invent an entirely new word to go in its place. These are perhaps the two most widely differing views on Anglish, and there exists many possible interpretations between them, depending on a writer's personal view.
This question was asked on the wiki: The Anglish Moot.