Shor is a quantum algorithm developed by mathematician Peter Shor in 1994. It is designed to efficiently factor large integers, which is a significant challenge for classical computers. The algorithm's ability to break down numbers into their prime factors has implications for cryptography, particularly for systems like RSA that rely on the difficulty of this task for security. The significance of Shor's algorithm lies in its potential to compromise current encryption methods. If large-scale quantum computers become available, they could use Shor's algorithm to factor numbers quickly, rendering many encryption techniques vulnerable. This has led to increased interest in quantum computing and post-quantum cryptography.