Infra Constructions receive a contract for construction of a building, and following terms were agreed...

In the contract term, the buyer agrees to pay the contractor the cost of doing project plus a profit. This is an example of cost-plus pricing arrangement.

On the other hand, "Fixed-pricing arrangement" often refers to lump-sum contract or supply/service contract with fixed price. "Incentive pricing arrangement" and "Gain-share/pain-share arrangement" have the same meaning. In this type of arrangement, both supplier and buyer agree on a target (it can be cost, or lead time, or quality, etc). Once the supplier reaches that target, it will be rewarded with a portion of the gain that the buyer gets, and will pay the price if it fails.