A grossup is a payment which makes a
net amount equal to the corresponding
gross amount. (That is to say, equal to the gross before the grossup.)
The term is almost exclusively used in the context of gross and net income, compensating for taxes. Expatriate workers may be able to swing a grossup provision in their contract, effectively allowing them to avoid double taxation or the high rates of their host country (After all, why support the Swedish welfare state out of your own pocket if you're just here for a 2-year tour of duty in Stockholm?). Of course, nothing prohibits employers from offering a grossup domestically, as an incentive for in-demand workers.
Financial instruments may also include grossup provisions, which serve to insulate investors from changes in tax laws or code, encouraging investment in a climate of uncertainty or instability.
Of course, as grossup payments themselves are not exempt from taxation, a simple grossup will not fully compensate for taxes, and so further payment may be required to reach full net-gross equivalence.