Where a variable is visible. Dim inside a procedure is local to it; Private at the top of a module is shared by that module; Public at the top of a standard module is global.

Code

Private counter As Long   ' module level
Public Const APP As String = "Model"

• Local

  Sub A() Dim x As Long ' only in A End Sub → x exists while A runs

  The default.

• Module level

  Private counter As Long ' top of module → Shared by every procedure in the module

  Module state.

• Global

  Public Const APP As String = "Model" → Visible from every module

  Global settings.

• Prefer local variables and pass values as arguments; globals make bugs hard to trace.
• Module-level variables keep their value until the workbook closes or code is reset.
• Public variables in a sheet module are accessed as Sheet1.name.

• Two modules with the same Public name conflict.
• Pressing Stop or editing code resets module-level variables.