1. Similar to the emoticon o_o but with an extra underscore (_).

Upper case Os are used more often to denote more shock than lower case Os.
Generally used in the same fashion (shock, look of bewilderment, blank stare, skepticism, or weirded out). However, the extra underscore is added to denote more stronger emotions.
2. Also may be used when an o_o may not want to be repeated.
1. Person 1: I found out I was adopted
Person 2: o_o

2. Person 1: And that I'm really a robot
Person 2: o__o

Person 1: It all came to me when I fell off a cliff and into a girl's house
Person2: O__O
by Guest3 June 18, 2011
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o__o is the shape of the Google Pixel 3XL's layout inside the massive runway of a notch.
Did you see Google's o__o? You could land a plane on it!
by Axle182 October 16, 2018
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