Rather than textual letters, the Chinese language is made up of ideograms, which are pictures that depict words and phrases. Notice the ideogram in the header area of this site. The top figure is an ideogram for qi. This particular ideogram for qi is composed of an upper radical that represents rising vapor and a lower portion which denotes grain. The steam that rises from a bowl of hot rice symbolizes distilled essence, thus qi can be translated as the vapor of the finest matter. Generally, qi refers to resources the human organism consumes, transforms, and transmits.

The bottom figure is an ideogram for gong which can be translated as meaning work, or cultivation. Thus, qigong can be translated to mean the cultivation of qi.
There have been various methods by which non-Chinese scholars have come up with to represent the sounds of these ideograms, while using Western letters to do so.

The Wade-Giles system was the first widely used system for converting Chinese ideograms to Western characters, but has since been joined by other systems, such as the Pinyin system, because of greater standardization.

The Pinyin system has become the most widely used system for representing Chinese ideograms in Western letters, because it has set international standards, whereas the Wade-Giles system was being used differently in different parts of the world.

Throughout this qigong site the Pinyin system is used in most, but not all cases. Thus you are more likely to see qi, rather than ch’i, which is the Wade-Giles form of Westernization.