This message is used to:

• request a specific Security to be traded with the second party. The request security can be defined as a multileg security made up of one or more instrument legs
• request a set of individual securities for a single market segment
• request all securities, independent of market segment

A subscription for security status can be optionally created by including SubscriptionRequestType (263) on the message.

See "Security Definition, Security Status, and Trading Session Message Scenarios"