Technical debt is the extra work that future changes may need because a team chose a quicker or simpler solution today. For example, a rushed workaround might solve a problem now but make the next update harder.
The word “debt” is a comparison: like borrowing time, you may need to spend more effort later. A shortcut is not automatically bad; sometimes speed matters. The useful thing is to know where the shortcuts are and decide whether improving them is worth the effort.