Your Lightroom License key is,
1. Cross platform Mac and or Win.
2. It is a single user / owner.
3. You can have two installations active with one in use at any point in time.
4. There is no deactivate process like other Photoshop products.
5. You can uninstall / install as many times as you need as long as you keep the spirit of the license.
6. The license key is specific to the Lightroom version, i.e License key for LR 4 will not work for LR 5.
7. You can upgrade i.e. purchase from any version of Lightroom 1,2,3,4 to the latest LR 5.
Thanks, I have a Lr v. 5 version and key. Will Adobe let me download Lr onto my new iMac? All I see is a Creative Cloud free trial. ??? Sorry for my ignorance!