Rule 1415 A writing may be authenticated by evidence of the genuineness of the handwriting of the maker.

If you have a document and need to prove it is real, one way to do that is by showing the handwriting on it belongs to the person who wrote it. This is called authenticating the document.

For example, if someone claims a letter was written by a certain person, you can bring in proof that the handwriting matches that person's known handwriting. This could come from a handwriting expert, or from someone who is familiar with how that person writes.