The character Qi (sometimes written Chi) has no simple one word equivalent in English. It has been translated as life energy, lifeforce, or energy flow, but definitions often involve breath, air, gas, or relationship between matter, energy, and spirit. Dr Yang Jwing Ming (Chinese physicist and taiji teacher) defines it as “bio-electromagnetic energy”.
Gong (sometimes written kung) actually means time or effort. In this context skill, mastery or cultivation would be more appropriate translations.
Therefore internal energy cultivation exercises would be the one of the easiest ways to translate the term into English. In China the term can be used to describe a wide variety of exercises ranging from meditation to conditioning exercises for martial artists. It would include all of the Chinese Internal martial arts (Taiji, Xingyi and Bagua). In the west the term is usually used to describe stationary exercises practiced for health and qi development.
There are literally hundreds of different types of qigong so it is difficult to generalize about what they look like. General principles include slow relaxed abdominal breathing combined with yin and yang openings and closing of the body, biomechanically efficient posture (i.e straightening the spine and aligning the joints) and smooth flowing movements. Some qigong involves stretching tendons and ligaments in a way that massages the internal organs.