A dike or sill is when a finger of molten rock penetrates through regular cooled, hard rock. If it's going in the same direction as the bedding plane, it's a sill. If it cuts across several of them, it's a dike.
A fault is when there's a really big crack that turns a bedding plane into two pieces, and one piece shifts position relative to the other piece.
is the sort of sight that would make your average roadside geologist swerve off the road while staring in fascination. That's a dike (or sill) that got cracked up into fragments. It's next to the Hoover Dam in Nevada/Arizona, where the land looks like it went through so much violent upheaval that there's no bedding plane at all anymore, it's all been crinkled into rubble. I imagine it's great fun trying to piece together what happened, and how, and in what order.
Note: I was on foot. No motorists or pedestrians were harmed in the taking of this picture. Also: click on the picture to get the full effect of its scale; those metal things at the top are electricity towers.