In C++, the Standard Template Library (STL) provides a set of generic algorithms that can be used to manipulate and process container elements efficiently. STL algorithms are implemented as template functions, which can operate on a wide range of containers and data types. These algorithms can be broadly classified into several categories:

1. Non-modifying sequence algorithms: These algorithms do not modify the contents of the container, and include operations such as searching, counting, finding the minimum or maximum element, and comparing two sequences.

2. Modifying sequence algorithms: These algorithms modify the contents of the container, and include operations such as sorting, reversing, copying, filling, and removing elements.

3. Partitioning algorithms: These algorithms partition a sequence into two groups based on a specified criterion, and include operations such as partition, stable_partition, and nth_element.

4. Sorting algorithms: These algorithms sort the elements in a container based on a specified criterion, and include operations such as sort, stable_sort, and partial_sort.

5. Binary search algorithms: These algorithms search a sorted sequence for a specified element, and include operations such as binary_search, lower_bound, and upper_bound.

6. Set algorithms: These algorithms operate on two sorted sequences and perform set operations such as intersection, union, difference, and symmetric_difference.

7. Heap algorithms: These algorithms operate on a sequence and transform it into a heap, which is a binary tree data structure with a special ordering property.

STL algorithms provide a standard and consistent interface that makes it easy to use different containers interchangeably in the same code. They also provide a powerful and efficient way to manipulate container elements, and can be used to implement custom algorithms and data structures. STL algorithms can be combined with STL containers and iterators to create complex and efficient data processing pipelines.