SCEP allows the automatic provision of client certificates via a SCEP server and a certification authority. This type of certificate is automatically renewed before it expires and can be used for purposes such as network authentication (e.g. IEEE 802.1x).
A Microsoft Windows 2008 Server (MSCEP, NDES) for example can serve as a queried counterpart (SCEP server and certification authority).
More information can be found at Microsoft Technet, e.g. in the comprehensive article Network Device Enrollment Service (NDES) in Active Directory Certificate Services (AD CS).