O(N^2) quadratic time complexity is a measure of how an algorithm's execution time increases as the size of the input data grows. Specifically, in quadratic time complexity, the time taken by the algorithm is proportional to the square of the number of elements (N) in the input data set. This type of complexity is common in algorithms with nested loops, where each element in a collection is compared with every other element.
While O(N^2) algorithms can be easy to implement and understand, they are not efficient for large data sets due to their slow growth rate in execution time.
Quadratic time algorithms are best used when the data set is small, and simplicity is more important than performance. For larger data sets, more efficient algorithms with lower time complexities, such as O(N log N), might be more appropriate.