1. A misspelling or improper allocation of a bunch of words
2. A correct sentence sent to the wrong person
Typically done when typing or texting.
The sentenco generally goes unnoticed until someone points out your error. This makes you feel a bit silly while also showing the other person to be the uptight dickwad, who doesn't let things slide, that he/she is.
Sometimes, one doesn't focus on one's grammar, punctuation, check the recipient, or simply has to many chat windows open; when that happens and you are made aware, you know you had a sentenco.
Randomly sms from Guy 1: I had better not see your scrawny ass if you don't bring the 30$ you owe me!
Guy 2: dude, feel like I'm missing half a conversation here. whats up?
Guy 1: Sorry man. Sentenco.
Girlfriend: I got an sms from you today calling me Heather and saying how you'd be free tonight when you told me you were sick in bed!
Boyfriend: Shit. Totally the worst time for a sentenco!