In the past, the definition of an achievement has been very rigid: it’s something large that you accomplish. However, this is a very broad definition, and is not necessarily the best definition one could come up with. Nowadays, employers, colleges, and business owners are looking for something special in those they select, something more than just your grades in school.
When updating your resume, an achievement nowadays could be anything from community service hours, to pet sitting for a long period of time, to being elected to Student Council. When looking at your life, anything that shows that you have experience can be treated as an accomplishment that one could post to KudosWall, thereby adding it to your resume.