What is technical debt?

In a sentence:

Anything about your code and development environment that slows you down.

• unclear, unreadable code
• lack of
  • test automation
  • build automation
  • deployment automation
  • and anything else that could be automated but you do manually today
• duplicate code
• tangled architecture and unnecessarily complex dependencies
• slow, ineffective tools
• uncommitted code and long-lived branches (hides problems that will slow you down later)
• important technical documentation that is missing or out-of-date
• unnecessary technical documentation that is being maintained and kept up-to-date
• lack of test environments
• long build-test cycle and lack of continuous integration