With Smart Card security, a user must have a physical card that provides access. Computers may come with smart card slots where users can enter their smart card for validation. Smart card works by having a digital certificate which ties a specific smart card to an individual user.
Smart cards are often used with another authentication method. For example, you might need to enter your smart card and provide a PIN number as well.
The US Federal Government uses a PIV (Personal Identity Verification) card, which usually has the employee picture and identification information.
The US Department of Defense uses a CAC (Common Access Card).