What are side-chains? What does it mean side-chains?

[Lucacrebbe]

Hello, sorry can you  please  explain to me what   are  side-chains, and    how   could  they improve the blockchain experience?

I really  don't  know  so much  about  side-chains

What are they?

What does it  mean ''side-chain''?

Basically is  it  a  ''personal  block-chain''?


Also  (anothere question):  do   stratis or  Waves    have their  own side-chain,   or not?

 Here  on the forum some people say they have that  stratis  and waves have their own sidechains, others  saythat  they do not have their own side-chains... so where is the truth?