The FULL SCAN hint forces a table scan for a given table. In this case, the optimizer does not proceed to evaluate if there are any other indexes that can be used to build the access plan or whether a table scan is better for the given query.
Example:
SELECT --(* vendor(SOLID), product(Engine), option(hint) -- FULL SCAN TAB2 *)-- * FROM TAB1, TAB2 WHERE TAB1.INTF = TAB2.INTF;