Final answer:
Shear (transform) boundaries occur when plates move sideways past one another, such as the San Andreas Fault in California.
Step-by-step explanation:
The type of boundary that occurs when plates move sideways past one another is called shear (transform) boundaries.
Transform boundaries, also known as shear boundaries, are characterized by plates sliding horizontally past each other. The San Andreas Fault in California is a prominent example of a transform boundary.