The Mac operating system currently supports applications that are both "32-bit" and "64-bit". Starting with macOS High Sierra 10.13.4, applications that are 32-bit will produce a one-time alert when opened. The alert means that the application will eventually no longer run in its current version on your Mac.
Apple has been supporting 64-bit applications, which can access dramatically more memory and enable faster system performance, for many years, so most applications you use are probably already 64-bit. However, some apps are still in 32-bit format and will stop working in the not-too-distant future, which will probably be with the next major operating system release.
Some of the 32-bit apps on your Mac are supplied by IT and we will take responsibility for determining how best to proceed with them. For apps you have acquired on your own, you should contact the developer to ask if they will be providing a 64-bit version. If not, you will need to look for an alternative program that will meet your needs.
Note that the warning message will only appear on Macs with macOS 10.13.4 or later, but ALL Mac computers will be impacted by this change.
For more information about how to check your operating system version, how to find out what 32-bit applications your computer has, and other important information, see:
Information Technology Service Desk
104 Job Hall
servicedesk@ithaca.edu
607-274-1000
https://www.ithaca.edu/intercom/article.php/20180420153101885