VLK stands for Volume Licensing Key, which is a volume licensing arrangement provided by Microsoft & others for schools & similar places so they can install it on many computers under the one license key.

As you have such, it's likely the version of Office you have was provided to you when you were either in the employ or a student of a school or similar or someone gave it to you. The license becomes inactive if you leave the organisation or the VLK gets cancelled.

This Wikipedia website might help you understand the VLK system.

Volume licensing - Wikipedia

Things are OK here although we have a govt. that urgently needs to be turfed out.