Frank's description of gross and net is quite right. But 'Net of ...' is not a phrase I have ever heard. It sounds very ambiguous to me i.e. it could mean either. It would also be very unusual (here at least) to specify a net pay, rather than a gross pay. If you are going to base a decision of a job on that, I would definitely ask to have that clarified!

It means that actual pay will be $100,000, but the gross pay will be $100,000 + applicable withholding tax. Let's say withholding tax is $25,000. The gross pay would be $125,000, which would leave $100,000 after withholding tax is taken out.