Subsampling data: terminology
This is more likely a question of what the data reporting application is trying to achieve, rather than a DSP question. 

Yes, there is a different term for Gate or Window. In fact, if you "subsample" and low pass filter, as per your first intuition, then you are effectively doing decimation. For more information please see: http://en.wikipedia.org/wiki/Decimation_%28signal_processing%29

The rest of your suggestions would be equivalent to subsampling followed by non-linear filtering such as median, min, max which would have the corresponding effect on the reported data. 

For example, a sliding window median filter would "absorb" any spikes in the reported data and the min and max filters would tend to report the highest or lowest values. For more information please see: http://en.wikipedia.org/wiki/Nonlinear_filter and http://en.wikipedia.org/wiki/Median_filter

So, it is really a matter of what does that GUI element try to convey to its user.

Hope this helps.

Supplementary Information:
Yes decimation does imply a stable sampling frequency but most DSP operations can be defined over irregular domains as well.

Irrespectively of that however, I think that we are indirectly looking at the real problem here which is one of visualisation.

The real problem, or at least my understanding of it so far, is that you are trying to convey a comprehensive view of a window of the history of a signal at a rate lower than its actual rate of change. Furthermore, this signal is not used in any further computation. If that is mostly accurate and assuming that your signal is coming from a stochastic process then no single value will be able to represent this history reliably.

Therefore, I would suggest two alternatives:


To use a single boxplot that would represent your last signal's frame
history in a comprehensive way including its min, max, median and
quartile information. For more information please see:
http://en.wikipedia.org/wiki/Box_plot
To convey the signal's history to your user via a Sparkline which
could furthermore be annotated with min,max,median lines. Please note that Sparklines can also be created via the use of special fonts, which makes them really easy to quickly insert to a GUI. For more
information please see: http://en.wikipedia.org/wiki/Sparkline and https://www.fontfont.com/how-to-use-ff-chartwell or http://nsfmc.github.io/chartjunk/


Hope this helps