Optimization means finding the parameters which make for the best possible solution of a problem. If you want to travel by car from A to B in the least possible time, the shortest road is not always the right answer. You need to take into account, for instance, if the road is congested. Therefore, a longer way may let you arrive faster. Finding this answer involves a "travel-time" optimization.
In many technological, industrial, commercial or scientific areas it is often the case that solving a problem involves parameter optimization.