To append means to add something to the end of something else. When you append a postscript to a letter, you're adding extra thoughts after you've already signed off. When a teacher appends additional problems to a homework assignment, she's tacking them on at the end.

The word is usually used in situations where the order matters. You normally don't append something to the beginning or middle; you put it at the end. A scientist might append new data to the end of her research notes. An author might append a glossary to the back of a book to help readers understand difficult terms.

In everyday writing, you might append a note to the bottom of a permission slip, or append a “P.S.” to an email when you remember something after finishing the main message. Computer programmers frequently append information to files, adding new lines of data without changing what was already there.

The word suggests something being attached or joined on, not woven throughout. When you append something, you're expanding what already exists rather than starting over or making big changes to the original.