Euclid's statement that all right angles are equal to each other is a postulate. A postulate, also known as an axiom, is a statement that is accepted without proof and serves as a basis for reasoning and constructing geometric proofs. Euclid's postulates are the foundational principles of Euclidean geometry, which is the study of geometry based on Euclid's work "Elements."

Here's a breakdown of the answer:

1. Euclid's Postulates:
Euclid's "Elements" consists of a series of books, where he presents his axioms or postulates, definitions, and propositions. Postulates are basic assumptions that are considered self-evident and do not require proof. Euclid's postulates are fundamental statements about geometry that he accepted without proof.

2. The Postulate in Question:
One of Euclid's postulates states that "if a straight line falling on two straight lines makes the interior angles on the same side less than two right angles, the two straight lines, if produced indefinitely, meet on that side on which are the angles less than the two right angles." In simpler terms, this postulate states that when a line intersects two other lines and the interior angles on one side of the line add up to less than two right angles (180 degrees), then the two lines will eventually meet on that side when extended.

3. The Equality of Right Angles:
Based on this postulate, Euclid deduced that all right angles are equal to each other. A right angle is defined as an angle that measures exactly 90 degrees. Since Euclid's postulate tells us that when two lines intersect, the interior angles on one side add up to less than 180 degrees, it implies that the remaining angle must be a right angle. Therefore, Euclid concluded that all right angles are equal.

In conclusion, Euclid's statement that all right angles are equal to each other is a postulate, which is an assumption accepted without proof in Euclidean geometry. Euclid's postulate regarding the intersection of lines allowed him to deduce the equality of right angles. This understanding serves as one of the foundational principles of geometry.