What exactly is dc offset and when would someone need to use this.
Actually, it doesn’t 
The “DC offset” option in Ardour doesn’t relate to removing a DC offset present in the signal.
It refers to an approach to tackling denormals - extremely small sample values, typically generated by plugins like reverbs that generate a long, decaying “tail”. On Intel processors, these cause substantial slowdowns in processing. One approach to fixing the issue is to add another very small value, which gives a result out of the “denormal range” where this causes an issue. (Note: the values we are talking about are orders of magnitude below the noise floor).
More information on denormals and audio processing: Floating point denormals | EarLevel Engineering
Ardour also has other options for tackling denormals, including hardware-based options such as treating all denormal values as zero.
You would only use the DC offset option if experimenting with approaches to tackling denormal problems on your system, and only if the hardware based options are not working (unlikely).
So the DC offset is used to fix other issues. Should the name be changed
The name accurately reflects the details of that selection. You are sure you are talking about the same thing Paul referenced, in the Preferences menu under the Performance window, “CPU/FPU Denormals” the checkbox for “Use DC bias to protect against denormals?”
That seems pretty specific in that context.
The term in the Ardour preferences is “DC bias” not “DC offset” which is why I ask if you are referring to the same thing. You did not provide any context to your question, was it referring to that Ardour menu selection, or did you see the term somewhere else? If you are just asking in a general sense, it is when the average of an alternating waveform is not 0, as explained in different wording in the links from bachstudies. You do not want that with audio, but the audio interface typically takes care of that for you, not something you have to worry about.
My apologies I may have gotten them terms mixed up. I have always heard the term DC offset referring to I think when the audio waveform is not lined in the Center or something like that. I assume ardour had a fix for this via a tool or button in settings like other programs too. For the denormal thing I understand that’s a different thing.
Yes, that is what bachstudies referenced. I have never found it to be a problem, any decent audio interface will not have any noticeable DC offset.
If you do end up with a track which has DC offset for some reason, just put a high pass filter on it and set the filter to the lowest cutoff. With the ACE highpass/lowpass filter included with the Ardour binaries, just click the lowpass filter slope control and set to off, and on the highpass set the cutoff frequency to 5Hz. Since DC is just a synonym for 0 Hz it will get removed by the high pass filter.
Some equalizer plugins have a highpass, lowpass included as part of a more full featured plugin so you might have something with highpass already available on a track, if not just add one of the specific purpose plugins as the first pre-fader plugin on the track.
For the record, you would be amazed at some of the interfaces and audio systems I have seen DC offsets through for the record, don’t assume just because you have a decent interface you are immune.
SeabladeI have never found it to be a problem, any decent audio interface will not have any noticeable DC offset.
Some people prefer audio interfaces that can deliver DC offset to their outputs, mostly modular synths people and laser people, to control gear that talks DC - also known as CV for Control Voltage. The main brand that comes to my mind is MOTU. So actually, any decent interface should not output DC when there is none intended
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