What do the Boost. Loyalty, and Transferable mean on the cards in DC?

Boost is a new mechanic entirely. You pay the Boost price (whatever number comes after the word BOOST), and you get that effect for that round. Boost is paid for with your resource points, so you can only pay boost during your recruitment phase.

Loyalty is a new keyword for the old, recruit only if you have another xxxxxx character card, where xxxxx = some affiliation.

Transferable is an expansion of an existing mechanic in the game whereby you can transfer certain equipment from one equipped character to another during the beginning of your formation phase. Prior to DC, only Stretch (Reed Richards) allowed you to transfer equipment, but now you can transfer any equipment as long as it has the keyword transferrable on it.