To target (対象 Taishō) a card is to select it as the recipient for some effect.
The word "target" was introduced in WXDi-P00 INTERLUDE DIVA and its associated decks, the first sets of Diva Selection. Additionally, all cards before Diva Selection that chose a SIGNI or a card in a public zone, such as Hisui, Natural Crystal, have had their wordings changed to say "target."
The Shadow keyword prevents a SIGNI from being targeted by the opponent.