Organic Search:
"...unpaid listings that appear in Google Search results..."

Direct:
"When a user searches for a business or brand directly on Google..."
"...typing the URL directly into the address bar, using autofill, or entering an address manually....indicate that people are intentionally seeking out a website."

Referral:
"...visits to a website that come from sources other than Google's search engine. This includes traffic from social media, email, and other websites.."

Paid Search:
"...pay-per-click (PPC) ads, are ads that appear at the top of Google search engine results page...sponsored..."

Unrecognized:
"...reference traffic sources or mediums that GA4 doesn't recognize..."

Organic Social:
"...unpaid traffic that comes from social media platforms like Facebook and Instagram..."