SQL Server: What does the NOLOCK query hint do?

Answer 1

This is the basic syntax of using NOLOCK
Select *
from Table with (NOLOCK)

It will give you data even if any transaction is still perfrmoing in Table. You can get incosistent or dirty data by this, but query performence will get increased.

Answer 2

With NOLOCK hint, the transaction isolation level for the SELECT statement is READ UNCOMMITTED. This means that the query may see dirty and inconsistent data.