What if any, is the difference between a band or a group?

No absolute difference, depends how music industry would call them.
G

     A group of pandas is called an embarrassment.  I can vouch for the appropriateness of this name after taking 4 of them to Chucky Cheeses for Elmo's birthday. 
      Three or more geese flocking on the ground is a gaggle; three or more geese flocking in the air are a skein. Here are a few more off the top of my head:

• Cattle: mob or herd
• Cheetas: coalition
• Colts: rag or rake
• Deer: herd or parcel
• Dogs: litter (if they're puppies), pack (if they're wild), or cowardice (if they're curs)
• Dolphins: pod
• Donkeys: pace
• Elephants: herd, parade, or memory
• Elk: gang
• Ferrets: business, hob (male), jill (female), kit (babies)
• Foxes: leash, skulk, or earth (this is the oddest of all group names in my opinion)
• Giraffes: tower
• Gnus: implausibility
• Goats: trip, drove, herd, flock, or tribe
• Gorillas: troop or band
• Hedgehogs: array
• Hippopotamuses: thunder or bloat
• Hyenas: clan or cackle

     Oh, did you mean musical groups and bands?
Sorry,
 Tim

How about this?
A band strongly implies that the members play instruments, aside from just singing and dancing. The Beatles and U2 are examples of bands. A group can be any band. The Beatles and U2 are also groups. But a group can also refer to performers who don’t play instruments onstage (or in a music video). These performers primarily sing and/or dance.

Would groupies be considered a group?