Both are acceptable for Access.

An MDB is (can be) a set of tables containing information that is
controlled and/or updated by forms within itself or another MDB or an
MDE or some other mechanism. It can also be a set of forms and reports
etc. for which all of the tables are linked into it. As an MDB it and
its reports/forms can be modified if full blown Access is used to open
it.

An MDE is  the same as above BUT which does not allow modification of
any of the forms / reports contained within it. It is sort of similar
to an executable, but requires either full blown Access or a runtime
Access to execute from. Even if full blown Access is used to open it,
it does NOT include any modifiable forms/reports.

Ron.