It meant the same as it means now. A surplus is when you have more of something than you need.
In ancient times, they built grainaries to store grains.
money
Surplus mean excess in business. A business can have a surplus of product in its inventory, which isn't good for revenues.
The ancient egypts ecomomy is based on surplus and crops
A surplus account is the accumulation of undivided profits.
Glass was traded as a surplus. They traded it for stone and wood
9 = IX in Roman times
they would barter it for other goods
Their empire provided a large revenue.
the oldern ciivvilization of eygpt
Depends on what you mean by ancient times. A safe bet is Egypt, Babylon, India (Indus valley) and China.
Surplus is extra.