tldextract accurately separates a URL's subdomain, domain, and public suffix, using the Public Suffix List (PSL). Say you want just the "google" part of https://www.google.com. Everybody gets this wrong. Splitting on the "." and taking the 2nd-to-last element only works for simple domains, e.g. .com. Consider http://forums.bbc.co.uk: the naive splitting method will give you "co" as the domain, instead of "bbc". Rather than juggle TLDs, gTLDs, or ccTLDs yourself, tldextract extracts the currently living public suffixes according to the Public Suffix List. A public suffix is also sometimes called an effective TLD (eTLD).