are held in hand until you wish to play them, at which point they enter play, generate their effect, and leave play. Because they do not persist in the field of play, they are "transient" cards.
are the other kind of transient card in the game. However, not the contrast in that
have a phase restriction limiting which part of the round they may be used in (the Action Phase) and they also have
as a timing indicator, meaning they may only be played as an
.
Cards fall within one of four timing categories in
Traveller (this information is available in the Timing section of the rulebook):
1) If an effect requires a cost (of any kind, not just credits. So, for instance,
) to be paid or a card to be played (for instance, a
. Though this is a bit messy, because
is technically a cost, which contrasts with simply no cost), then it is what is called an
Activated Effect. Absent any other restriction, an Activated Effect may be generated at any time, however only effects with
may be generated during/in response to another effect.
2) If an effect is on a Permanent (:connection,
,
,
,
,
) and has no cost at all, then it is what's called a Persistent Effect. Persistent effects can be Conditional (so they require a certain value or game state to exist) or Unconditional. Persistent effects are always active, unless subject to an unmet condition.
3) If an effect has a Phase Restriction, then it may only be generated during that phase.
4) If an effect has a timing indicator, that defines both when and how the effect may be generated. For instance, only
effects may be generated in response to/during a pending effect.
These categories are not necessarily mutually exclusive. You may have an activated ability that operates under a phase restriction. See page 24 for an example.
I realize it can seem confusing at first. Timing is usually the most sophisticated and complicated part of any card game's rules, in part because while the vast majority of situations resolve fairly intuitively, there can be special occasions that require recourse to finer distinctions of when things technically happen.