A Long Block is a series of eight weeks between Short Blocks. There is a block calendar on this wiki.
Role Playing Games in a Long Block generally last the entire duration. Some games span several Long Blocks. and often additional Long Blocks, but rarely into subsequent short blocks.
Games for a long block are proposed by the middle of the preceeding short block and voted on in week 2 of the short block. The votes allocate players to games on a best-fit basis. GMs of the games in the next long block then have two weeks to prepare for the game.
Occasionally a game started in a Long Block start early (perhaps for character generation for a new game) or spill over into the following short block (if sessions were missed during the block). However, people try to avoid both of these.