No they are not exactly the same thing. By saying merger people mean a situation where two companies become one and the new company keeps things (like the management, the systems, the production lines, the brand name) of both the old companies.
An acquisition on the other hand is when a company buys an other company which can mean that the management can change and the brand name can change. It does not have to be the case but the common practice is that when an acquisition takes place, the acquired company is absorbed by the acquiring company.
On the other hand, when a merger takes place, both companies are involved in the way that the new company will be run the next day.