Attribution
Organic search
Also called SEO traffic.
Organic search is visits from unpaid results on a search engine. The visitor clicked a normal listing, not an ad.
How it is measured
A session is labeled organic when the referrer is a known search engine and no paid tag is present. Paid clicks carry an ad tag or an auto-tag, which sets them apart.
Check it by comparing analytics organic sessions with the clicks in the search console. They will not match exactly, but the trend should move together.
Worked example
A tax-accountant's site gets 4,300 organic sessions in February and 1,750 in June. The search console shows impressions down 44 percent for the same months.
The match between the two reports confirms the fall is seasonal and not a tracking loss. A page that lost its ranking for 'estimated tax deadlines' in April shows up in the console as the single large drop.
How it differs
Organic search is unpaid. Paid search is bought by the click. The channels share the same engines and often the same queries, but only the second has a cost per click.
Common errors
Counting every search visit as SEO. Missing paid clicks without tags. Reading a drop as lost rankings when it is a tracking change. Ignoring other search engines. Using it as a proxy for brand strength.
In practice
Compare analytics with the search console monthly. Check that paid ads are tagged so they do not inflate organic. Look at the landing pages that drive most organic sessions.