What is meaning of +- 4D in eye for job application requirement

power 4dSYNCHRO Construction Solution - SYNCHRO 4D Power BI Data Connector - Prerequisites Setting up Global Environments SYNCHRO Control Permissions Using Connector TableTwo lenses have power of (i) + 2 d (ii) -4D. What is the nature and focal length of each lens? b. An object is kept at a distance of 100 cm from lens of power -4D. Calculate the image distance.