In the example shown on the right, both hydrogen molecules, (and both fluorine molecules) are on the same side of the carbon chain. As the carbons are joined by a double bond, these cannot rotate around the molecule.
See Geometric isomerism for more on this.
In genetics, cis- is a prefix used in terms such as "cis-regulation" to signify the co-location of two or more genes on the same chromosome of a homologous pair.
In mathematics, eix = cos x + i sin x (see Euler's formula). Cis is a now seldom used abbreviation for "cosine plus i sine" (of x). Usually eix or exp(ix) is best used.