The ANY and ALL operators allow you to perform a comparison between a single column value and a range of other values. For instance:
select * from Table1 t1 where t1.Col1 < ANY(select value from Table2)
ANY means that the condition will be satisfied if the operation is true for any of the values in the range. ALL means that the condition will be satisfied only if the operation is true for all values in the range.
To use an example that might hit closer to home, doing this:
select * from Table1 t1 where t1.Col1 = ANY(select value from Table2)
Is the same as doing this:
select * from Table1 t1 where t1.Col1 in (select value from Table2)