Can you explain what constant time complexity of data search means and in what cases it is achieved?

Constant search complexity (O(1)) means that the time to find an element does not depend on the size of the collection — it is always approximately the same. This is achieved, for example, in hash tables, where an index is computed based on the key, and access to the element occurs directly. However, in the worst case (collisions), the time may increase, but on average, the search is considered constant.