The act of engaging in multiple text communications simultaneously while keeping track of gossip and not texting the wrong person some awful regrettable text you can't take back.
Always pay attention when multitexting, you dont want to rehash last weekend's debauchery to grandma. Oops.
The act of having 2 completely different conversations with the same person by utilizing more than 1 messaging app. Usually a result of a text left unresponded too, then followed up by a text best sent in a different fashion (a text sent, then later a picture sent on snapchat)
Steve on snapchat: Hey what do you think you got on that test?
*10 minutes later
Steve on a text: Hey do you think fish talk to each other
Jason on snapchat: don't know you?
*Sent just after
Jason on text: bro I never even thought about that
Steve on text: Bro this is some prime multitexting
Both conversations continue but with completely different subjects and never cross over