If you have long phrases or complicated words that you are using frequently in your document, you may want to have them appear automatically in Word when you type something more simple. So say, for example, you are writing about pituitary dependent hyperadrenocorticism. Instead of writing this out all the time you could type PDH and have word automatically expand this to pituitary dependent hyperadrenocorticism. This video from KeyStone Learning Systems explains how to use the autocorrect feature in Word to do this.
Word’s autocorrect feature for things you are sick of typing