Single Client Access Name (SCAN) is a single name that allows client connections to connect to any database in an Oracle cluster independently of which node in the cluster the database (or service) is currently running. The SCAN should be used in all client connection strings and does not change when you add/remove nodes from the cluster. SCAN allows clients to use EZConnect or the this JDBC URL.

sqlplus system/manager@ sales1-scan:1521/oltp

jdbc:oracle:thin:@sales1-scan:1521/oltp

The SCAN is defined as a single name resolving to 3 IP addresses in either the cluster’s GNS or your corporate DNS.

Reference:

http://www.oracle.com/technetwork/products/clustering/overview/scan-129069.pdf