Ki

Definition
(genetics) Gene knock-in, as in genetic engineering method
(chemistry) A symbol for the dissociation constant of an inhibitor
(chemistry) The measure of bond-tightness between an enzyme and a corresponding enzyme inhibitor
(chemistry) The measure of ligand binding affinity
(chemistry) Potassium iodide
Supplement
In genetics and molecular biology, Ki stands for gene knock-in, or simply knock-in. A knock-in pertains to the genetic engineering method involving the insertion of a protein coding cDNA sequence at a particular locus in the chromosome of an organism, typically a laboratory mouse model.¹
In chemistry, Ki is a symbol for the dissociation constant. By definition, the dissociation constant is a mathematical constant that describes the tendency of a large molecule to dissociate reversibly into smaller components. It is the equilibrium constant in a dissociation reaction. It is a type of equilibrium constant that specifically involves the measure of the propensity of dissociation of a complex molecule into its subcomponents. An example of its application is to describe how tightly a ligand binds to a particular protein. It is also referred to as the equilibrium dissociation constant or the ionization constant.
Reference(s):

¹ Gibson, Greg (2009). A Primer Of Genome Science 3rd ed. Sunderland, Massachusetts: Sinauer. pp. 301–302. ISBN 978-0-87893-236-8.