Poached is a term used in ultimate to signal to teammates that someone on offense is wide open and the thrower can easily throw it to them without exerting a lot of effort.
Poaching occurs at all levels of ultimate. It occurs when defenders are tired and can also occur when there is a lot of confusion amongst the defenders on who is supposed to be guarding who. At high levels of ultimate defenders can purposely move away from their man, aka poaching off from the cutter/handler to try to trick the thrower into thinking that man is open. Defenders can also poach off their man to prevent a more threatening option from developing.
This step shows one of the most basic forms of poaching or being poached. All the defenders on the field are guarded against except for? Defenders 2 and 7 are not with their man; defender 2 is far away from cutter 2 and 7 is far away from H3. In this case, the best option for H2 is to throw it to either H3 or cutter 2 as both of them are wide open.
What's most important is that either 2 or H3 (or people on the sideline) recognize that they are open, and they should be screaming out "I'M POACHED!!!" or "2 is POACHED" or "H3 IS POACHED!!!" This is to get H2's attention to see that someone is wide open. In this case since H3 is wide open and is an easy throw, H2 will throw it to H3.
H2 now throws it to H3
The key thing to take away from this lesson is to observe the field while you are playing. A lot of people have tunnel vision or they only look at the disc. It is important to view the rest of the field and recognize who is wide open. Once that is recognized, scream out to everyone else on the field that this specific person is poached. This will help the handler with the disc to look specifically for that person.
An effective defense can also use poaching to make things harder for the offense to throw the disc up the field but that will be taught in another lesson.