To oscillate means to swing back and forth between two points or positions in a regular, repeated pattern. Picture a playground swing moving forward and back, forward and back. A pendulum in a grandfather clock oscillates steadily, and that regular motion helps the clock keep time. Electric fans oscillate by turning from side to side so they can cool a wider area of the room.

The word works for physical movement, but it also describes switching between two different states, opinions, or feelings. A student might oscillate between confidence and doubt before a big presentation, feeling sure one moment and nervous the next. During a close basketball game, the lead might oscillate between the two teams as first one scores, then the other.

Scientists use this word frequently because oscillation is everywhere in nature: sound waves oscillate through the air, light oscillates as it travels, and even atoms oscillate.

The key to oscillation is its regular, repeated nature. Something that merely moves around randomly isn't oscillating. True oscillation has rhythm and pattern, swinging reliably between two points or states.