What is a herbarium and what is a herbarium specimen?

Do you ever remember picking a little flower, then placing it inside a book? After a few days, you would find a dry and completely flattened flower. With a bit of care, this flower could be stuck down on a board and will remain in this state for hundreds of years. Now if you took the time to write a little note next to your flower, recording the date that you collected it and where you found it…then this is what you could call a specimen.