Real image

Rays from a common point are reflected or refracted and then intersect, in the CED's word. Not appear to intersect. Light energy genuinely arrives at the image location, which is why holding a card there shows a picture and why a projector works.

The sign test. Solve $\dfrac{1}{s_i} + \dfrac{1}{s_o} = \dfrac{1}{f}$ and read the image distance. A positive $s_i$ is a real image: in front of a mirror, or on the far side of a lens from the object. You never have to recall which arrangements give which type.

What makes it the opposite of a [virtual image](/glossary/virtual-image) is what is physically present, not the arithmetic sign. A virtual image sits where no light ever goes, reconstructed by your eye from diverging rays, and a screen there catches nothing. For a single optic with a real object the two also split on orientation: real images are inverted, virtual images upright.

Which optics can make one. Only a converging optic, and only with the object farther out than the focal point: a concave mirror or a converging lens with $s_o > f$. A convex mirror and a diverging lens never do.

Real does not mean enlarged. Move the object beyond $2f$ and the real image is smaller than the object; between $f$ and $2f$ it is larger. Size is a separate reading, from magnification.