Excellent question! (I moved it under Visual ReCode / Questions because your example shows a Visual ReCode license in particular.)
The Activation Limit is the currently set limit of how many separate machines can be activated on that license key. So, in your example, you could activate it on three separate machines before it would stop you. Trying to activate a fourth machine would then be blocked by the license server.
Visual ReCode is licensed per-user (the number of Licensed Copies). Each licensed user can then install and use Visual ReCode on any computer for which they are the primary user. For example, you might have a desktop at work, a company laptop, and a personal computer which you also use to work from home. If you need to activate more than the current limit, you can contact us and briefly explain the need, and we can extend it for you. If you need activations for another user, an additional user license would need to be purchased to increase the number of Licensed Copies.
Sometimes machine upgrades or replacements can leave behind an activation which is no longer needed but still takes up an activation slot. The administrator registered with the license can remove obsolete activations on the "my" site (such as on my.visualrecode.com) in order to free up more slots, or you can also contact Support (such as emailing to email@example.com) for help with this.
What does the activation limit mean?
Can I install the software in three different machines?