A right angle measures 90° and is found at the corners of rectangles and squares. Students identify right angles in their environment (door frame, corner of paper) and distinguish them from angles that are smaller (acute) or larger (obtuse).
From your earlier work on angles, you know that an angle is formed wherever two rays share an endpoint, called a vertex. You likely noticed that angles come in different "openings" — some look like sharp corners, some like wide sweeps, and some sit at exactly the corner of a square. That square-corner angle is special enough to have its own name and its own symbol: the right angle.
A right angle measures exactly 90 degrees. The degree symbol (°) measures how open an angle is: 0° would be completely closed, and 180° would be a flat, straight line. Right angles sit exactly halfway between those extremes, producing a perfectly square corner. You can find right angles almost anywhere in the built world: the corner of a sheet of paper, the corner of a door frame, where a wall meets the floor, the intersection of a plus sign. Architects and carpenters depend on right angles constantly — a room whose corners were not right angles would be very difficult to use. On a diagram, a small square drawn at a vertex signals "this angle is exactly 90°."
With a right angle as your reference point, the other angle types follow naturally from comparison. An acute angle is smaller than 90° — its opening is narrower than a square corner, making it look "sharp." An obtuse angle is larger than 90° but smaller than 180° — its opening is wider than a square corner, making it look "blunt" or spread out. The words come from Latin: *acutus* means sharp, *obtusus* means blunt. A straight angle is exactly 180°, which looks like a straight line with the vertex somewhere in the middle.
The practical skill is visual classification: look at an angle, compare it mentally (or physically) to a right-angle corner, and decide which category it belongs to. The corner of any index card or piece of paper works perfectly as a portable right-angle checker. Hold the corner to the angle in question — if it fits exactly, the angle is right; if the angle is smaller, it is acute; if it is larger, it is obtuse. You will use this classification constantly when studying triangles, quadrilaterals, and coordinate geometry in future courses.