Deployment
The process of initially setting up or later updating a live website. There are lots of components (server configuration, code, database, files, permissions) and steps involved so that such a deployment task can take a while and needs to be executed very carefully to make sure it doesn't break anything. Deployment can be done manually - which is not recommended - or automatically. With automation it is very easy to also include additional tasks like testing and pre-processing into the task and the expected result is always going to be the same. Nothing gets missing and it will only always happen, if all conditions (tests, coding standards, etc.) are met.
As a team that had spend time and money for years in developing best practices for staging, deployment and operations of many Drupal sites on version 5 to 7, the all new Drupal 8 came with some surprises and challenges in 2015, when first alpha and then beta releases started to see the light. Where all of Drupal core up to Drupal 7 had been exposed in the main project folder, all the contributed code from the Drupal community and third parties was located deep down in the code tree with custom code for the specific project sometimes was hard to separate from other contributions.