SENT protocol output unit is LSB. What does this mean?
It does in fact mean LSB or, alternatively, the measurement amount corresponding to 1 LSB.  The specs you're looking at are measurement ranges.  The numbers given are the highest and lowest readings you can expect.  Note that they're 12-bit readings, meaning they have a potential (positive) range of 0 to 4095.  4095 what?  Depends how it's calibrated, but to skirt that quagmire, they call it a LSB and spec those ranges accordingly.  It's kind of like using "percent of full scale" as a unit, but the fact that it's already digitized makes LSB a natural unit.