ACT(REP) : Action is replace the existing one
ACQUIRE(USE) :locks on table and table space are imposed when it executed sql statement
RELEASE(COMMIT) :locks on table and table space are released on commit.
VALIDATE(BIND) : the authorization is validated at bind time.
EXPLAIN(NO) : no display of access path
Replace the existing one means u have executed the program with abc.plan and u have done some modifications in the pgm and again if u submit it with the same plan name it will give error as it is already existing....Action(replace) will take care of the execution of the pgm without errors