自行车(zì xíng chē) - bike, bicycle in Mandarin

自行车 (zìxíngchē) is "bicycle, bike". 自行 (zìxíng) means "by oneself, on one's own" and 车 (chē) is "vehicle", so it is literally a "self-propelled vehicle", the machine you move under your own power rather than an engine's.

The verb that goes with it matters: you 骑自行车 (qí zìxíngchē), "ride a bike", using 骑 (qí), the verb for anything you straddle, never 坐 (zuò), which is reserved for vehicles you sit inside like a bus or car.

The casual, everyday word in speech is often the shorter 单车 (dānchē) in the south and Hong Kong, or simply 车 (chē) in context when it's obvious a bicycle is meant. 自行车 (zìxíngchē) is the standard, textbook-correct form used on signs and in writing, so it is the safe choice to produce yourself.