What is a repository? What is a metapackage?

[Richard Owlett <rcowlett@cloud85.net>]

A goal of the Debian installer is to create a system that can be used by 
*ALL* people to use for *ANY* possible purpose.

I find the resulting system:
  1. consumes more disk space than necessary.
  2. consumes excessive bandwidth during installation.
     [I have a low monthly cap on my internet connection.]
  3. installs packages I whose function I don't need/want.
  4. doesn't install functions I routinely use.
  5. installs packages that unsatisfactorily perform needed functions.
     [I have to install additional packages.]

I plan to get around these problems by creating a local repository and 
several very custom metapackages. My internet search turned up tools to 
create and/or modify both.

I did not find authoritative descriptions of the structure of either 
repositories or metapackages.

Where do I find such?
TIA