IdGlobal

IdTimeoutDefault is a constant Integer value that indicates the default timeout value should be used in methods that initiate connection, reading, or writing to remote computer systems. IdTimeoutDefault indicates that timeouts occur based on the underlying protocol stack implementation, instead of relying on the read or write methods in the Indy library. 

IdTimeoutDefault is often used as the default value for a timeout argument supplied to methods in the Indy library. 

Use IdTimeoutInfinite to indicate that timeout values should not be used in the corresponding method.

IdTimeoutInfinite 

TIdSocketHandle.Readable 

TIdIOHandler.ReadLn