Orphan describes a block that has been abandoned and will not be built upon.
Blockchain is technology for creating permanent, secure digital recordings. If you imagine the blockchain as a book of records, then each page in that book is what is known as a “block”. A block is simply a recording of information. Blocks are attached to each other making what is known as the blockchain. Because many computers are maintaining the blockchain, occasionally two blocks are created at the same time. Since only one block can be created at a time, only one will be continued and built upon, the other block will be abandoned and is known as an orphan.