When you use the Less than (<) sign in a database search, you're saying you want to find all records that have values less than, or before the criteria you set.
For example, setting the criteria <1000 will return all records with values less than 1000, not including 1000 itself.
With dates, you will get results before the criteria you set. So <01/01/2000 will return all dates before, but not including, the 1st January 2000.