When it comes to engines, the term "deleting" refers to the removal of one or more of the emissions control devices that the engine came with. When an emissions device is "deleted", the device and any other relevant components in question are physically removed and the engine is then re-tuned to run without said device.

"Deleting" is different from "defeating" in the sense that "deleting" refers to physically removing emissions devices, but "defeating" involves disabling emissions devices while leaving all of them in place on the engine. For example, an EGR (exhaust gas recirculation) cooler can be defeated by welding it shut in some spot or blocking it off from one or both ends by inserting a metal plate between the cooler and the exhaust or intake manifold. DPF's (Diesel Particulate Filters) can be defeated by being drilled out or by installing bypass pipes.

On Diesel engines, people who do deletes will typically remove EGR (Exhaust Gas Recirculation) systems and DPF's (Diesel Particulate Filters), as these two systems are infamous for drastically increasing a Diesel engine's fuel consumption.
Here in Michigan we no longer have any kind of emissions testing, which means that today you can find quite a few deleted Diesel trucks, and even some cars and SUV's, running around in the state.
by The_Anonymouse June 22, 2021
To eliminate something/someone
by Zdragov June 18, 2019
'Delete' can have several different meanings and is very context dependent, here are just a few examples:

When you have demolished your food - deleted
When you have completed a task - deleted (a film/degree/project)

When your friend has scored/died in the club - deleted

A: Hey James, is that beer you have in your hand!?
J: Yeah Austin, a beautiful pils it is
A: Delete it!

J: *look of disdain in his eyes, but also respect - proceeds to drink beer in one go*
by Mr. Deleted May 07, 2019
To delete someone is to defeat him/her in a video game so hard that their account gets removed and their head explodes
Bro you just deleted that bitch from the entire fucking game
by NydriAyo May 13, 2018
What the one guy from the popular japanese anime Deathnote says when he is writing down names in the deathnote
Guy from Deathnote: DELETE!!! DELETE!!! DELETE!!!
by JISUNGPARK March 25, 2018
The button that only Hillary Clinton can properly use, much to everyone else's disapproval.
Clinton will be the first F president. (that was meant to say female, but someone decided to delete the emale! jajajajajaja!)
by Intelligence001 July 17, 2016
To be killed, most notably by gunshot.
Man if you keep talkin' Imma have to delete you!
by aceOFspade May 19, 2011
verb- to throw away something unnecessarily
1. MOM!! Why did you delete the leftovers?!? I was gonna eat them!
2. Awww man! I wish i hadn't deleted that perfectly good couch.
by Bambie3223 October 28, 2010