[Kimitri]

It may be a regional thing but I have never heard ”bit rot” refer to legacy code. In the retro computing circles bit rot refers to hardware defects (usually floppies or other storage media) caused by cosmic rays or other environmental hazards.

[Leparamour]

I have to agree with Kimitri here. This is the only context in which I have ever encountered the term 'bit rot'.

[MayeulC]

I agree this is the primary context, but I've seen unmaintained (or very old) software being reffered to as "bit rotting" by extension. As in, forward compatibility might break due to obsolete dependencies, etc.

[superjan]

Yeah looks like I was confusing “software rot” and “bit rot”.

https://en.wikipedia.org/wiki/Software_rot