In Python, a NameError is raised when a program tries to use a variable that hasn't been defined or assigned a value, often due to misspelling or premature access. The error message specifies the problematic variable and the line of code causing the issue. For example, using an undefined variable 'x' in a range() function results in a NameError. To resolve this, ensure the variable is defined with a value before use and is correctly referenced in terms of spelling and case. Correcting the example by defining 'x' as 5 before using it in a loop allows the code to execute successfully. Additionally, tools like Rollbar can help manage and troubleshoot such errors by offering real-time tracking and analysis, simplifying the process of fixing Python errors.