Need help with keyboard issue

Can I get rid of the strange select0r. Unsure what o did to bring it. Probably an accidental keystroke.

Driving me mad.

oSX ten point eight point three

TIAoo

Well, rebooting fixed the issue -- thank goodness... But now my productivity has been derailed. Any ideas about what happened, and how to solve it for next time?

Thanks in advance for your attention.