What is 'spendability of coinbase transaction after 100 blocks' in Mastering Bitcoin referring to? Ch7 of the book writes at the end of the Introduction section:


  "After 100 blocks back there is so much stability that the coinbase transaction—the transaction containing newly mined bitcoins—can be spent"


Can someone explain what is the author trying to convey with an example?
This part of the book is referencing blockchain reorgs (reorganization). This occurs when a node determines that it is no longer validating the longest chain.  When a node sees that there is a new longest chain on the network it moves over and begins verifying the blocks.  This can cause previously mined blocks to be orphaned.  Often times this only occurs at the tip (the last couple of blocks) of the blockchain.  When a block is a 100 deep into the blockchain, the risk of a reorganization that goes back that far is very unlikely, and, therefore, it is very unlikely that the block will become invalidated (orphaned).