I've been reading the design goals and I see they refer to "daughter-chains". What are these, and are they different to side chains?
The esperanto term for daughter chains is Moneridos. Daughter chains are pegged side-chains which can be merged mined. They are designed to process microtransactions and other stuff that would just spam the main chain, like on-chain betting or gambling.
The differences to side chains are that they are deeply anchored into the Monero Core and will be enabled on any Monero node. Also, the plan is that they do not have any coinbase transactions. According to @fluffyponyza, tokens on daughter chains are only to be created on-demand when there are pegged transactions into the sub chain.
Read more at this reddit scalability discussion.