Wiktionary
alt. A white, opaque fluid, applied to paper to mask textual errors; used especially to mask errors in typing so that corrections may be overtyped n. A white, opaque fluid, applied to paper to mask textual errors; used especially to mask errors in typing so that corrections may be overtyped
Wikipedia
A correction fluid or white-out, is an opaque, usually white fluid applied to paper to mask errors in text. Once dried, it can be written over. It is typically packaged in small bottles, and the lid has an attached brush (or a triangular piece of foam) which dips into the bottle. The brush is used to apply the fluid onto the paper.
Before the invention of word processors, correction fluid greatly facilitated the production of typewritten documents.
One of the first forms of correction fluid was invented in 1951 by the secretary Bette Nesmith Graham, founder of Liquid Paper.
With the advent of coloured paper stocks for office/typing/photocopier use, correction fluid manufacturers began producing their product in various colours, particularly reds, blues and yellows, so that corrections made on these papers would be less visually invasive.
Usage examples of "correction fluid".
He blanked out the chicken scratches of the legitimate physician with typist's correction fluid and photocopied the blank prescription form.
But then all that he's done is to get a bottle of correction fluid, change the date, and create a new accident, just like that.
When you type the wrong letter, you paint over it with correction fluid, wait for the fluid to dry, then type the right letter.