Living Card Game and LCG are registered trademarks(®) of Fantasy Flight Games. The main goal is to provide a Collectible Card Game experience without using random booster packs as distribution method.
Every LCG has one Core Set. It usually provides multiable decks playable out of the box, and various game aids like token.
LCGs are expanded due to Premium Expansions and Cycles. Each Cycle contains 6 Packs released monthly. Deluxe Expansions and Packs contain play sets of the cards released with it, as opposed to the Core Set which only contains one copy of every card released with it.
Core Sets and Deluxe Expansions stay tournament legal forever, but cycle - as the name implies - cycle out of the format. Once the 8th cycle is added to the format, the first two cycles are removed from the format.