It's a form that calculates the deductible part of any passive loss or loss carryover you may have in your return.
The loss could stem from rental real estate, Schedule C self-employment, a k-1, or other passive activities. It may just be a continuing carryover from a prior year loss, but the deductible portion would have to be calculated again this year, even if the answer turns out to be zero.
Here's the list of expected forms availability dates, which will update if the date becomes sooner or later:
https://ttlc.intuit.com/replies/3319876