En stund is typically a bit longer than ett ögonblick (literally "an eyeblink"). And you wouldn't say "En stund!" to someone when you want to say "[Sorry,] one moment!".'
Ögonblick and stund can both be translated to "moment", but stund can additionally also be translated to "[a] while".
From shortest to longest, you've got
- Ett ögonblick - a moment
- En stund - a moment or a while
- Ett tag - a while (longer than stund)
The suggested translation (which is the version you can see on top of this page) is ett ögonblick. However the machine tries to match your input to the closest accepted answer. For instance if you happened to put en instead of ett with ögonblick, you might get the suggestion en sekund, since sekund is an en word.