What does it mean by pruning and enrichment in the case of Rosenbluth method?

Question

[user366312]

As far as I understand:

1. Pruning means deleting something.
2. Enrich means to enhance/increase weight.

Now my question is, in the case of PERM algorithm,

1. Are we deleting some polymers chains? Or, are we deleting some beads in all polymer chains?
2. Are we increasing the weights of some polymers? Or, are we increasing the weights of some beads/atoms of all polymers?

When we are modifying the pruned weights, what are we replacing them with?