Keys can be symmetric or asymmetric depending on the algorithm.
From the standpoint of a non-technical user, they're not any different in nature; a password and a private key are both just strings that give full access to your account. One is easier to remember (password), one is harder to remember (key). The one that is harder to remember usually ends up in a Google doc, iCloud, or saved as a text file.
Heck, here's one: "kty": "EC", "alg": "ECDSA_w_SHA256", "crv": "P-256", "x": "xYkEVgMClD28hXHn5JQjrgjRX3crmr0OhGiWKsLvxUY=", "y": "5lZZGFF6VrVubIHfRhGbvQBGpw6LcbP3/ZBVk7PqH0Y="
It's what you'd get if you somehow got into the db and decrypted it.
Now, do feel free to give me your nice symmetric secret password, since it's the same, yeah?