Concept:
Modulus of Rupture is a measure of the maximum bending stress a material can withstand before breaking.
Step 1: Tiles are brittle ceramic products.
Step 2: Their strength is commonly tested under bending load.
Step 3: In the MOR test, a tile sample is supported and load is applied until fracture occurs.
Step 4: The calculated value gives flexural strength.
\[
MOR = \text{Flexural strength}
\]
Step 5: Hardness, plasticity, and abrasion resistance are different properties and are tested by different methods.
Therefore, MOR test measures:
\[
\boxed{\text{Flexural strength}}
\]