Review products are rated out of ten which is then converted to a score out of 5 stars.
The ratings out of 5 usually denote the following:

1 star (0-2/10)
A poor product. It probably looked awful, performed badly and would not be recommended to anyone.
1.5-2 stars (3-4/10)
This product is useable; barely. Low performance and average looks or vice versa.
2.5-3 stars (5-6/10)
An all round average product.
3.5-4 stars (7-8/10)
A good product with some minor discrepancies that could be improved upon. Recommended.
4.5-5 stars (9-10/10)
An almost perfect product. Fulfilled all of our expectations and could only be improved in the slightest of ways.