Definitions of tip
an extra payment given in addition to a required payment, usually to express appreciation for service (US=gratuity)
In American restaurants the customary tip is 20%.
important, non-public information given to an investor about a share
The allegation is that Smith sold his stock acting on an unlawful tip received from his broker.
information provided to the police to help in preventing or solving a crime
The police received a tip that a large shipment of narcotics would be arriving at the port at 11 AM on Thursday.