Modular is a keyword ability.
The second of which means that when the affected creature dies, you can move all of its +1/+1 counters onto another target artifact creature.
Agria casts an Arcbound Worker, as it enters the battlefield it enters with one +1/+1 counters (as Arcbound Worker has modular 1). Later in the game she puts an additional two +1/+1 counters and then Arcbound Worker dies, when it dies she can move the three +1/+1 counters from it onto another target artifact creature.
- 702.42a. Modular represents both a static ability and a triggered ability. "Modular N" means "This permanent enters the battlefield with N +1/+1 counters on it" and "When this permanent is put into a graveyard from the battlefield, you may put a +1/+1 counter on target artifact creature for each +1/+1 counter on this permanent."
- 702.42b. If a creature has multiple instances of modular, each one works separately.