What does TOP 1 mean in an sql query?

Question

What does TOP 1 mean in an sql query?

SELECT TOP 1 RequestId 
FROM PublisherRequests

Answer 1

I disagree with "The order will be defined based on the clustered key in that table."

SQL Server Books Online is quite explicit: If the query has no ORDER BY clause, the order of the rows is arbitrary

a repro demonstrating that this is not always the case: Without ORDER BY, there is no default sort order.