Track Changes is (yes, singular is correct here!) a feature in Microsoft Word which allows you to keep track of the changes you make in a document. Anything you delete is shown with a line through (struck out) while anything you add is underlined, usually in red. Track Changes is also known as redlining; this is because in the days before email and computers, proofreading would be done by hand on a hard copy of the document, and a red line would be drawn to indicate where changes had been made.
Here is an example of an edited text with Track Changes:
Traditionally, it was
job f the proofreader in the publishing industry to check the typset copy (the version of an authors manuscript after it ben typedand the text
presented d in the page to create the finished book) The proofreader check s the text for typogrphical errors, print errors etc. . using standard proofreader ’s marks, which would be drawn in the margin next to the relevant line. It ’s considered a specific skill that must be learnt. Someone not trained in proofreading mightnot see specific errors such as missing words or print
And here it is again, with those changes made (the final or 'clean' version):
Traditionally, in the publishing industry, it was the proofreader’s job to check the typeset copy (the version of an author’s manuscript after it had been typed by the typesetters and the text presented on the page to create the finished book). The proofreader would check the text for typographical errors, print errors, etc., using standard proofreaders’ marks, which would be written in the margin next to the relevant line. It is considered a specific skill that must be learnt. Someone not trained in proofreading may not see specific errors such as missing words or print errors.