The term HSP has been used in many research papers while describing BLAST output. What are High Scoring Pairs (HSP)? I'm not very successful in Googling.
http://www.ncbi.nlm.nih.gov/books/NBK62051/

> A High-scoring Segment Pair (HSP) is a local alignment with no gaps
> that achieves one of the highest alignment scores in a given search.