This is the easiest thing to understand — it’s the same animal in both languages. It filters out result sets/subgraphs. Not all predicates have an equivalent in the other language, but the concept is the same.

SQL Query. 

SELECT *
FROM "Person"
WHERE "Person".age > 35 AND "Person".hair = 'blonde'

Cypher Query. 

START person=node:Person('name: *')
WHERE person.age > 35 AND person.hair = 'blonde'
RETURN person