what is the meaing for "mostly latch-free SCN"

I see "latch free" in my database, the P2 is 166.

What is the meaing for "mostly latch-free SCN" ?

How to reduce this event ?

SQL> select * from v$latchname where latch#=166;

    LATCH# NAME                                                                   HASH

---------- ---------------------------------------------------------------- ----------

       166 mostly latch-free SCN                                            1282175915

SQL>