Moneropedia
Block
The Basics
A block is a container of transactions, with a new block being added to the blockchain once every 2 minutes (see constant DIFFICULTY_TARGET_V2 defined as 120 seconds), on average.
Blocks also contain a special type of transaction, the coinbase transaction, which add newly created Monero to the network.
Blocks are created through the process of mining, and the node that successfully mines the block then broadcasts it to each of the nodes connected to it, who subsequently re-broadcast the block until the entire Monero network has received it.
Fake or bad blocks generally cannot be created, as nodes that receive blocks always verify the transactions they contain against a set of consensus rules that all nodes adhere to, including validating the cryptographic signatures on each transaction.