Four words are given, out of which three are same in a certain way while the rest one is different. Find out the different one.

The answer is C. Area.

A square, triangle, and rectangle are all shapes. A square has four sides of equal length and four right angles. A triangle has three sides and three angles. A rectangle has four sides, two pairs of parallel sides, and four right angles. Area is a measure of the amount of space enclosed by a shape.

The difference between area and the other three words is that area is a measure, while the other three words are shapes.