White Box, like Black Box, is a test design method. Tests based on the internal logic of the application are called White Box tests. White box testing is often more thorough, but also much more time consuming than Black box testing and requires some knowledge of development processes.
White Box often talks of Code Coverage, which is where the code itself is covered by test cases. There are several levels of Code coverage.
Statement Coverage: In order to achieve statement coverage, each statement of the code has to be covered by a Test Case.
Branch Coverage: The testing of each branch condition. For each branch statement, each branch of the statement must be performed by a test case in order to achieve branch coverage.
Path Testing: If every distinct path is covered by a test case then path coverage is achieved.
The goal of code coverage is often unrealistic with anything but the smallest of systems as it takes a long time to analyze the program code. There are a number of different techniques to approach code coverage...
Source - softwaretestingsucks.com