Legacy code is code not under test - Michael Feathers
Legacy code is code you're afraid to change - Mark Seemann
Code where the intention isn't clear, and hasn't had any love - Anon
Code nobody wants to work on - Anon
Legacy code is code that makes you laugh and/or cry - Mark Jones
Refactoring: "disciplined technique for restructuring an existing body of code, altering its internal structure without changing its external behavior" - Wikipedia
Quick hacks to get something out there - Anon
Knowingly writing bad code to deliver something on time - Anon
Stuff what's difficult or risky to change - Anon
The difference between the application that you would like to build and the application you actually build - Martin Fowler
The effort it takes to refactor your code to make it easy to add the next feature non-invasively- Michael Feathers
Long-term architectural benefits are sacrificed for expedience
Not caring about solving known problems
The refusal to practice solutions that are otherwise widely known to be effective
Making poor decisions based on an easy answer
Modelling excessive details, resulting in excessive complexity
The result of failing to seek understanding
"Not Invented Here"