Technical debt
The implied future cost of rework caused by choosing an easy or quick solution now instead of a better approach that would take longer.
What it means
Technical debt is a metaphor, not a formal Scrum concept, describing shortcuts in code, architecture, or design taken under time pressure that accrue 'interest' in the form of slower future development.
Some technical debt is a deliberate, reasonable trade-off, taken with eyes open to hit a deadline; problems arise when it accumulates silently and is never repaid, degrading velocity and quality over time.
Common mistakes
A healthy Definition of Done and regular refactoring inside Sprints, rather than a separate 'tech debt Sprint,' are common ways Scrum Teams keep debt manageable.
Example
The team ships a hardcoded configuration to hit a launch date, then logs a backlog item to replace it with a proper settings page.