To interlock means to fit or connect together so firmly that the pieces can't easily come apart. Think of how you clasp your hands together, weaving your fingers between each other: that's interlocking. The fingers don't just touch, they grip and hold.

Lego bricks interlock when you press them together, with the bumps on top fitting snugly into the holes on the bottom. This creates a strong bond that won't fall apart if you pick up your creation. Gears in a machine interlock, with the teeth of one wheel fitting perfectly between the teeth of another, so when one gear turns, it makes the other turn too.

The word can also describe ideas or systems that depend on each other. In a mystery novel, the clues interlock to reveal who did the crime, each piece fitting with the others to complete the picture. When two people's schedules interlock, they mesh together without conflicts.

You'll sometimes see interlocking used as an adjective, like “interlocking pieces” or “interlocking rings.” The key idea is always the same: things that interlock don't just sit next to each other, they connect in a way that makes them work together as one strong unit.