Rainbow tables are a time-memory trade-off technique used to crack password hashes. Instead of brute-forcing each password guess and hashing it on the fly (time-intensive), you precompute a massive lookup table mapping hashes back to their plaintext inputs (storage-intensive). Rainbow tables sit in the middle — compressing the chain so you trade some CPU time for significantly less disk space.

Here's your comprehensive wordlist reference for hacking & cracking. This is a(n) article / guide on cracking & hacking with wordlists.