Upsizing is a feature of Microsoft Access for upgrading an Access database to a SQL Server database while still retaining accessibility through Microsoft Access.
Quote from Wikipedia:
Upsizing is the term coined by Microsoft to describe the process of upgrading Microsoft Access Database to a Microsoft SQL Server. This allows to continue using Microsoft Access as a database front-end whereas the actual back-end is served by a separate local or remote SQL Server allowing much higher productivity and data volumes. Microsoft Access from the version 2000 on has a special Upsizing Wizard which facilitates the data migration to the proprietary Microsoft SQL Server. No other RDBMS are currently supported for upsizing.