What makes code legacy?

What is it that makes code, legacy code?

As with plain legacy, when the author is dead or missing, you as a heir get all or some of his code.

You shed some tears and try to figure out what to do with all this rubbish.

By using hardware, software, APIs, languages, technologies or features that are either no longer supported or have been superceded, typically combined with little to no possibility of ever replacing that code, instead using it til it or the system dies.

Michael Feathers has an interesting definition in his book Working Effectively with Legacy Code. According to him legacy code is code without automated tests.