see Form 8949 for the meaning of these boxes
https://www.irs.gov/pub/irs-pdf/f8949.pdf
(A) Short-term transactions reported on Form(s) 1099-B showing basis was reported to the IRS (see Note above)
(B) Short-term transactions reported on Form(s) 1099-B showing basis was not reported to the IRS
this may also be worded A is "covered" and B is "non-covered" as referred to in your summary screenshot. The detailed sections may have this wording in the headings also.
