DBRM: It is Data Base Request Module which contains the extracted SQL query from the source code.
Plan: It contains the executable sql code and access path.
Package: It has the access path to access the table for its sql. To execute a DB2 program we need to have Plan but in some case we do have a package to reduce some complexity, like if a program has 4 sub program and if any one undergoes changes then we can bnid only the respective package used each package will have one DBRM and each DBRM will be created for each program. It reduces the cost of larger plan bind.
Collection: Group of packages are called collections.