Editing is defined as the process of correcting errors such as grammar, usage, spelling, punctuation, and capitalisation, to enhance the clarity and effectiveness of the writing.
Put even more simply, it is the process of putting something such as a literary work into an acceptably readable form.
Proper editing can also eliminate inconsistencies in style and format as well as spelling. An example is the ‘Americanization’ (or should that be Americanisation) of the English language. While both spellings are acceptable, I prefer the second one but imagine if you used a ‘z’ in one word and a ‘s’ in the same word elsewhere in your text. This kind of inconsistency is often hard to spot when reading your own copy but your reader will no doubt pick it up straight away!