What is an open ground and why would the neutral wire measure 50v?
When you see a phantom voltage like that, it's the hallmark of a sensitive meter. Though sensitivity sounds like a feature, most cheap meters have it too.  Disregard. 

Well, we can read a few things from the tea leaves.  

You know this wire runs near a "hot" wire for a little bit of distance - enough to pick up an SLF radio signal from the adjacent wire.  If you've ever built/used a crystal radio that uses a tiny earpiece and is passively powered (from the AM airwaves themselves), you understand tiny amounts of power can be induced from radio.  

You know this wire is rattling i.e. not connected to any supply.  You know in a North American panelboard you have 4 wires: L1 that's 120.4 volts to ground, L2 that's 119.6V to ground, neutral that's 0.4 volts to ground, and ground that's 0.0V to ground. (assuming a 0.4V neutral-ground drift; YMMV.)  You know two things from the rattling/floating wire.  


it is not connected to any of those (because if it was, it would read that voltage). 
it is not connected to a load whose other wire is connected to any of those (because if it was, the load would "pull the wire" to the voltage of the other wire.)