Discarding is the act of putting a card from hand into the discard pile during the Discard Phase. A player must discard if his/her hand is bigger than his/her maximum hand size, and s/he must do so until his/her hand is no longer above the maximum. When the Corporation discards, the discarded cards are put into Archives facedown.

Discarding is distinct from trashing, which refers to putting a card from any play area into the discard as part of a game action or effect.

Page 14, Column 2, Sidebar, Core Rule Book
Trashing and Discarding

A discarded card is not considered to have been trashed, and vice versa. Cards that prevent a card from being trashed cannot prevent a card from being discarded.

Page 14, Column 2, Paragraph(s) 4, Core Rule Book
Cards discarded from HQ are always sent to Archives facedown, regardless of whether they have been previously accessed by the Runner.
Page 30, Column 3, Paragraph(s) 3, Core Rule Book
Discard: The act by which a player moves a card to his trash pile at the end of his turn if he has exceeded his maximum hand size.
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