An update license is an annual subscription that is in effect for twelve (12) months.
When you purchase a maintenance license, you will be entitled to receive updates and upgrades. When new updates become available, you will be able to install them and keep your software current. An update license includes an upgrade rights, so you will be entitled to install and use new versions of the same products you initially purchased, as they become available. Note that the maintenance license covers only your purchased products (E.g., new version of Pro if you purchased the Pro version).
For example, you purchased ARC+ EXEcutive 2010. Later, a new release will be available with support of a newer DWG format. If you purchased a maintenance license you will be able to download and use the new release. When a new version is introduced, say ARC+ EXEcutive 2013, you will be able to install that version and you won't need to purchase an upgrade.