Symmetric cryptography
Cryptography where the same secret key both encrypts and decrypts. It is far less affected by quantum computing than public-key cryptography — Grover's algorithm only halves the effective key strength.
In practice
AES-256 retains roughly 128 bits of security against a quantum attacker, which is ample.
Related terms
A quantum search algorithm that finds an item in an unstructured set of N in roughly √N steps. Against symmetric cryptography this halves effective key strength — a nuisance answered by doubling key sizes, not a break.
The standard symmetric block cipher used for bulk encryption. AES is not broken by quantum computers: Grover's algorithm gives only a square-root speedup, so AES-256 remains secure and AES-128 remains adequate for most uses.
Cryptography using a mathematically linked key pair: a public key that can be shared, and a private key that must not be. It is the part of modern cryptography that quantum computers threaten most directly.