It stands for amortized bond premium. The answer below from one of our other agents seems to help a lot of people with this issue.
This response only explains that the ABP Adjustment comes from a 1099-INT. It does not explain where to find the calculation of the value. The program does not have a link to the data source, nor any help from the Data Source button. Aargh!
The link below explains the computation.
If you are using TurboTax online, you will not have access to worksheets until after you submit payment for the TurboTax software.
The reference link in this post is nice, but the program should have this explanation in the right-click "about interest adjustment", and it should have a "Data Source" link back to the calculation or source value.
irs.gov has a really good search dialog
so does Google
I used the DuckDuckGo search query irs abp adjustment and got more than 13 pages, most of which referred me to the irs.