I added http://blog.liquibase.org/2014/11/contexts-vs-labels.html for some additional background.
Labels can be added to changeSets the same as contexts.
The concrete use case behind adding labels was a company that is basically trying to get around not using version control branches. They want to label changeSets based on features (instead of creating a branch) and then selectively “merge” those features at execution time.
The idea of giving the deployment team the power to write complex logic is more general than that particular use case, which is why the more generic “label” term was created.