Exactly a licence key - which you could transfer to someone else. You didn't own the software. You owned a licence to use it.
A typical proprietary software licence text is irrelevant when it comes to terms of ownership, transfer of ownership, use of the good etc. as the law applies and determines "how [things] actually are". A contract, let alone a unilaterally dictated licence text, is legally unable to take away certain rights the consumer enjoys.