An open access band (or orchestra) is one where pupils at the beginning of their music making can be in an ensemble and make music together.
Normally these take the form of a wind band or orchestra. The bonus of doing it online is that any kind of instrument can join in – from violins to recorders, pianos to pots and pans percussionists.
Open access bands tend to use music specifically arranged or written for the ensemble to ensure it meets the needs of the musicians in the group, and to ensure it can be flexible. The Dragon March has been written with that in mind – plenty of options parts wise which can include people with absolutely no musical experience to those with higher grades!
Although the Dragon March (and this idea in general) is aimed at primary aged music makers, absolutely anyone can join in. If you have a higher grade on an instrument then be wary that the parts might seem quite easy to you – or alternatively, that some tricky flourishes might be added in to give you a challenge!