Cryptographic nonces

I saw “nonce” in the Bitcoin and Dogecoin code, so I wanted to learn about it. Looking it up, I see that a cryptographic nonce is a hash of a random number (?) sent from one computer to another, like a one-time secret password between compadres to get into the tree fort. Nonces make hashing harder for computers and somehow makes it more secure. I know that cryptocurrencies use nonces for “proof-of-work”, but I don’t know more than that atm.