"HOLP" is the abbreviation for "Held's object last position". Usually the HOLP updates every frame that Mario is holding an object, to the coordinates the object being held has, if an object is released the HOLP will stay at the last position and not update anymore.
Normally once a new object is being grabbed the HOLP will immediately update again, however in some cases the HOLP update can be avoided. The HOLP coordinates are not changing by changing the stage or area and will stay the same.

One case to prevent a HOLP update is by using another glitch called "Hat in Hand". Hat in hand can be achieved by having Mario's cap-put on animation being cancelled while a previous cap-put on animation is still playing. This allows to grab and release an object without updating the HOLP, thus this object will be sent to the HOLP coordinates and eventually this object will become unloaded if the new position is outside of the radius in which objects are loaded. Mostly the objects will not be able to be used as it takes too long for Mario to reach them after they have got loaded again but if you are using a warp or teleport within the level you can technically have enough time to use these objects again.

This was only one example for how to make use of HOLPs, there might be others as well but those are not going to be explained here.