Jaquard: The inventor of the punched card, which was used for weaving. If he'd taken out a patent the French would no doubt own the IT industry and we'd all have to refer to computers as ordinateurs.
JCL: An old mainframe idea. Originally JCL was a set of commands for scheduling and running programs in the right order. IBM kept on “improving” it. Eventually it became as complicated as a programming language, so mainframe users had to write programs to run programs. Great while it lasted; jobs for the boys, grist to the mill.
Kilobyte: In the early years of computing, computer memory was made from small magnetic hoops through which wires were threaded – eight of which were required to store a single byte. The hoops were sold by weight and thus the term Kilobyte was invented. It is now defunct as even short blog post will not fit into this amount of memory.
Kludge: Coined by Jackson W. Granholm to mean "an ill-assorted collection of poorly-matching parts, forming a distressing whole." There is no better definition for software than this.
Knowledge Management: The proper exploitation by a blackmailer of his information asset. Effective knowledge management can and often does lead to massive returns on investment.