LSB/unit or Unit/LSB is the factor(called sensitivity) with which you have to multiply the raw sensor data.
Say Sensor A has X,Y and Z registers ,
the values coming in each of the registers needs to be Divided/multiplied with the LSB/unit or Unit/LSB factor.
This is because the data sheet says @ the particular fullscale you will have this much sensitivity(LSB/unit or Unit/LSB)
for LSB/Unit :
x lsb means - 1 unit
1 lsb means - 1/x unit
value lsb(value in the register) = (1/x)*(value in the register) - Apply unitary method here.
similarly for Unit/LSB you have to multiply the sensitivity.
You can build Accelerometer,Magnetometer or Temperature sensor or may be Gyro-meter in one module, but what if a customer/User wants only one sensor?
Rgds,
Rp