Illustrator Clipping Masks
Extremely useful. Innumerable applications.
Start with any object; it can be a placed image, text, a line, a shape, anything… For simplicity, I chose a half-circle.
Draw any shape on top of it.
Select both, right click->Make Clipping Mask
Voilàs!
And the good thing is: Both objects remain in the figure. You can still adjust, move around, or delete both objects individually.
clipping, Illustrator, mask