In visual studio, some lines of code have light grey background while debugging

Question

What does it mean? I am debugging C# code.

Answer 1

Grey lines are statements which are on the call stack, including other threads' call stacks. In other words, statements which started, but have not yet finished executing, are greyed. Try clicking on various functions listed in the call stack + switching to other threads and clicking.

Answer 2

Those are the lines comprising the call stack other than the line for the current frame. Here's a picture:

_{(source: 280z28.org)}