Generally it’s a difference in pay based on location.
At my last job a friend moved from our Buffalo location to our San Francisco office and they gave him a raise of 15k to make up for the difference. Problem is once he got out there and started pricing houses and everything else that cost so much more than it does here he realized he was actually making less.
Salary in Buffalo NY:
$60,000
Comparable salary in San Francisco CA:
$97,046.98
If you move from Buffalo NY to San Francisco CA…
Groceries will cost: 29.128% more
Housing will cost: 211.573% more
Utilities will cost: 37.254% less
Transportation will cost: 9.952% more
Healthcare will cost: 33.411% more
So that 15k raise they gave him was basically a big pay cut.