CiviCRM is contributed to by hundreds of people: users who report issues/bugs/suggestions; implementers; developers; people who take time to offer advice on this site or on chat.civicrm.org.
It's useful for the project to have a measure of this, so we can appreciate everyone's input. As well as helping build a picture of the work that goes into improving CiviCRM over time, people who contribute enough hours can be listed on the find an expert page.
How can this be measured and how can I record my time?
(Note: I'm listing this here with an answer because the information was very hard to find.)