k5

K5 is a designation used in multiple disciplines. In mathematics, K5 denotes the complete graph on five vertices. This graph has five vertices and every pair of vertices is connected by an edge, for a total of 10 edges. K5 is a central example in graph theory and is nonplanar; by Kuratowski's theorem it cannot be drawn on a plane without crossings. A common drawing places the vertices at the corners of a pentagon and connects all pairs, producing a pentagram inside. K5 is one of the two minimal nonplanar graphs, the other being K3,3.

In astronomy, K5 is a spectral subtype of K-type stars in the Morgan–Keenan (MK) system. Subtypes range from K0 to K9, with K5 representing a mid-subtype. The effective temperature is roughly 4,000–4,500 kelvin, yielding an orange hue. K5 stars may be main-sequence dwarfs (K5V) or more evolved giants (K5III), depending on luminosity class. They are common in the solar neighborhood and are used in studies of stellar classification and exoplanets.

In automotive branding, K5 is used by Kia for a mid-size sedan marketed in several markets. In some regions it supersedes the Optima nameplate, reflecting regional branding changes. The Kia K5 emphasizes modern styling, updated infotainment, and enhanced safety features across successive model generations.