std::pair is a structural template that provides a way to store two objects as a single unit. The objects can be of different types.

Extremely useful in competitive programming and interview problems for returning multiple values from a function, or storing associated data in maps and sets.

• Access: $O(1)$ (via first and second members).
• Comparison: $O(1)$ (lexicographical).

cpp Standard
#include <utility>
#include <iostream>

std::pair<int, string> p = {1, "Forge"};
std::cout << p.first << " " << p.second; // 1 Forge

• Confusing first and second.
• Forgetting that pairs are compared lexicographically (first is compared, then second if first is equal).