Technically, The total of all assets, all debts, and other obligations of an
individual that will be subject to probate after a person's death. Estate planning, on the other hand, is a broader concept that includes planning for all assets and obligations and includes methods that pass outside probate.
For example, designating a beneficiary for a deposit account that will pass the funds in the account to a beneficiary automatically upon death would not be subject to the probate process supervised by the Surrogate's Court. However, using such a method would be considered part of your overall estate plan.