The strategy + the plan. Setting scope, timing and direction of the engagement.
To plan the audit so that it will be performed in an effective manner — overall audit strategy + detailed audit plan.
SA 300 sits in the Planning phase of the audit. The Standards on Auditing are issued by the ICAI Auditing and Assurance Standards Board (AASB) and deemed to be prescribed by the Central Government under Section 143(10) of the Companies Act 2013. Compliance with SAs is mandatory for every audit conducted by a Chartered Accountant in India.
For authoritative text, refer to the ICAI AASB Compendium of Standards on Auditing at icai.org.