What does `m_` variable prefix mean?

Question

I often see m_ prefix used for variables (m_World,m_Sprites,...) in tutorials, examples and other code mainly related

Answer 1

To complete the current answers and as the question is not language specific, some C-project use the prefix m_ to define global variables that are specific to a file - and g_ for global variables that have a scoped larger than the file they are defined.
In this case global variables defined with prefix m_ should be defined as static.

See EDK2 (a UEFI Open-Source implementation) coding convention for an example of project using this convention.