A hot block is a term used to refer to a block with fire underneath it. Generally, it refers to ones in a group of blocks, where Chip has to select blocks to either push or to use, and the wrong choice will cause his death. Examples include the south-east section of Block N Roll, the block area of Lesson 4 where the idea was introduced, and throughout Special.
Although there may be fire under a block, blocks will not be destroyed if fire is underneath them. They can start, be pushed onto, or even reveal fire hidden under the floor.
In Lynx, hot blocks are much easier to deal with due to block slapping.