This definition comes from the technical glossary.
The number of blocks preceding a particular block on a block chain. For example, the genesis block has a height of zero because zero block preceded it.
Block height — Bitcoin.org Developer Guide
Definition of block height — Bitcoin StackExchange
Why is block height required in the coinbase? — Bitcoin StackExchange
Is block height always sequencial? — Bitcoin StackExchange
Bitcoin.org is community supported: 3FkenCiXpSLqD8L79intRNXUgjRoH9sjXa