An AVLA / Connect Music Licensing License is a music copying license that your DJ should have if he is using any copied music compilations or hard disk computer playback system for your function.

You should ask your DJ if he has such a license and to show you this license before you decide to hire him or her.

Not ALL disc jockeys require this license but 99% of disc jockeys use self copied music compilations and as "commercial" users of music are not covered under the same laws as non-commercial users such as consumers who make copies for their own private use. 

Feedback DJs carry AVLA licenses and/or use music sources that have been legally channelled to ensure that all laws have been followed. No need to worry about your DJ being shut down during an event due to license infringement.