Sometimes the credit you give has a lifespan -- that is, you only want to vouch for the achievement for a certain period of time. After that, perhaps the recipient needs to demonstrate their worthiness for the credential again. A good example of credentials that might expire include: Professional credentials that are re-issued every two years after continuing education classes or exams are completed, or credentials representing awards given out annually declaring recipients reigning champions for the current year.
When you create or edit a credential, you have the option to set its expiration period. The option always default to credits that never expire. If you want to designate a time period for expiration, click "Add more detail" while creating a credential in the Credit Builder tool (under "Give" area of the site), and set the expiration accordingly in the "Expires" section. You can choose from days, months, or years and set the number accordingly.
The actual expiration date for a credential is automatically set based at the time the credential is issued to someone, and is based on the current date and time when the credential is issued. The expiration date will then show up when anyone looks at a recipients earned credentials, letting them know if the credential is still valid and active.