Shards are entities what appears somewhere. Players should lead the shard to their targets.
Shards can travel on links, and there are blue and green target portals. They are jumps in every 5 hours, this interval is depends on the event, determined by NIA.
If there is no link from the portal, after 4 unsuccess jump shard is jumping randomly near somewhere by current location. (This depends on the event too.)
Now a global event going. There are a lot of shards, and every shard is a piece of a character in the story of ingress by NIA.
Both faction wants to controll many character as they can by lead shards to their target. In this global
It is a style of gameplay of ingress. Check an intel map and try to locate them while game is going.
More and exact information is here:
Here you can follow the actual gameplay, and also a timeline from the begining of the event: http://thrakazog.com/magnus/#t=Maps