The penny-farthing was an early form of what transportation?

The penny-farthing, also known as a high wheel, high wheeler and ordinary, was the first machine to be called a "bicycle". It was popular in the 1870s and 1880s, with its large front wheel providing high speeds (large distance for every rotation of the legs) and comfort (shock absorption through the wheel). It became obsolete from the late 1880s with the development of the modern bicycle, which provided similar speed amplification via chain-driven gear trains and comfort through pneumatic tires, and were marketed in comparison to penny-farthings as "safety bicycles" due to the reduced danger of falling from height.

The name came from the British penny and farthing coins, one much larger than the other, so that the side view resembles a penny leading a farthing. Although the name "penny-farthing" is now the most common, it was probably not used until the machines were nearly outdated; the first recorded print reference is from 1891 in Bicycling News. For most of their reign, they were simply known as "bicycles". In the late 1890s, the name "ordinary" began to be used, to distinguish them from the emerging safety bicycles; this term and "hi-wheel" (and variants) are preferred by many modern enthusiasts.