Option Explicit should appear at the beginning of every code module in Access.
When Option Explicit appears, you must explicitly declare all variables by using the Dim Statement. If you try to use an undeclared variable name, an error will occur at compile time.
This will help you avoid spelling errors in your variable names.
The VBA editor has an option to force Option Explicit to be declared for all modules: Tools > Options
This is valid in Access 2016, not sure for previous versions.