Outer means located on the outside or farther from the center of something. The outer layer of an onion is the papery skin you peel away first. The outer planets of our solar system (Jupiter, Saturn, Uranus, and Neptune) orbit far from the Sun, while the inner planets (Mercury, Venus, Earth, and Mars) stay closer.

When astronauts prepare for a spacewalk, they put on an outer suit over their inner clothing to protect themselves from the harsh conditions of space. A castle's outer walls formed its first line of defense, while the inner walls protected the keep where people lived.

The word often pairs with inner to show contrast. Your outer appearance is what people see, while your inner thoughts and feelings stay private. Outer space refers to the vast region beyond Earth's atmosphere.

You might also encounter outer in phrases like outer limits (the farthest boundaries) or outer reaches (the most distant parts of something). When something is on the outer edge, it's at the very boundary, whether that's the outer edge of a circle, a forest, or even an idea.