Both distributions use a utility called debconf, that can handle preseed files which essentially do exactly as they say; preseed the anwers to the questions debconf may have.

Any particular line in a preseed may look similar to:

d-i partman-auto/confirm boolean true

The first keyword, d-i indicates the application debconf should use this line for. In this case, d-i is short for debian-installer.

The second keyword describes a category and question. In this case, the category is automatically partitioning, and the question is whether we want to confirm the autopartitioning the Debian Installer performs; true means we're saying: "Yes, confirmed" (not "Yes, we need to confirm please").