A bounded update is a triggered route update that is sent only to those routers that need the information. The purpose is to conserve bandwidth.
To supplement the answer from Victor it may help to understand "routers that need the information". The thing that makes the update bounded is usually summarization or perhaps route filtering. The update is propagated to all neighbors who should know that particular route. But at the point where that route gets summarized or that route gets filtered out then there is no need to advertise that prefix any further.
ip address 10.10.10.1 255.255.255.0
router eigrp 10
This will generate an advertisement for 10.10.10.0/24 to all neighbors of that router (they should know this route). Those neighbors will advertise that route (prefix) to their neighbors (they should know this route). Now assume that one of these neighbors creates a summary address for 10.10.0.0/16 on its interfaces. The neighbors out those interfaces have no need to know 10.10.10.0/24 but instead will need to know 10.10.0.0/16
Alternatively perhaps some neighbor has configured a distribute list to deny 10.10.10.0/24 out some interface. The neighbors out that interface do not need to know that route.
Does that help?
This will generate an advertisement for 10.10.10.0/24 to all neighbors of that router (they should know this route).
OK, that clears up that.
It's a language thing, you know...the words chosen...
As far as "need to know" routes, I guess it would be better stated as "allowed to know". IOW, the neighbors out that interface are only "allowed to know" the summary route.
I know it sounds like hair-splitting semantics, but in this case, a slight change in the words can confuse the issue considerably.
I absolutely agree with you that language and semantics are very important and frequently how we say things (the words that we choose) may help to clarify or may cause confusion.
I can see the alternative of describing it as "allowed to know" but I believe that there is a sense in which "need to know" is quite appropriate. In designing the network someone decides that certain neighbors need to know a certain level of detail (so that they will make appropriate forwarding decisions) and that other neighbors need to know less detail and will still make appropriate forwarding decisions.
 As I think about it part of where I am coming from is an aspect of decision making theory that asks: how much information do you need to make the right decision. I believe that underlies the appropriate design of the network.
The bounded update, is done when eigrp stablishes neighbor relationship, and whenever there is a changes on eigrp (periodic changes) and its a reliable.
the Query and the reply are also reliable handled by RTP.