A "clean slate" is a common phrase used in the English language to indicate having a fresh start with nothing bad taken into account. The saying is known as an English idiom, which means that people who speak English well know this combination of words means something other than the literal dictionary definition. People who are not as familiar with the English language might find idioms confusing; to someone unfamiliar with the saying, a clean slate might mean little more than cleaning a writing slate.
Oddly enough, the meaning of many idioms can be linked at least slightly to the literal definition of the words. Several other idioms include the word "clean" to emphasize the absence of negativity. For example, a "clean bill of health" means a person has no ailment whatsoever, while a "clean break" means that a person wins absolutely everything possible. The phrase a "clean slate" paints an image of someone wiping clean a chalk or marker board, making it blank to write something new. For the English language, this imagery has carried over to all aspects of life and is used to explain starting over anew and forgetting the past.
The US movie Clean Slate, released in 1994, is about a private eye who gets amnesia and then has to go to court about a murder. While it is a comedy, the storyline focuses on the fact that the main character wakes up every morning with a blank mind. The irony is that the clean slate actually works against him since he needs to remember what happened in the murder case. Most of the time, a clean slate is like a breath of fresh air to the person to which this saying pertains.
This particular saying is used a lot in relationships. In real life and on the television screen, broken relationships between friends, lovers, or coworkers often come to reconciliation with someone in the relationship offering to give the other a clean slate. Another situation in which people use this phrase is in describing someone who has had a bad past and wants to change his or her ways to make a better future. Situations that this applies to would include leaving behind bankruptcy, addiction, or even a criminal record. In this case, having a clean slate is important because whatever happened in the past had the potential to negatively affect the outcome of the future if not erased.