A home-made programmer, often originated from a trial-and-error design and often with very dubious performance. Sometimes works well with one chip model but not with another. Sometimes works well with one PC but not with another. May fail to correctly handle some input files (such as HEX files with holes in them) because the original designer ended the development as soon as the programmer was "good enough" for his/her specific task.

Tends to initially feel like a cheap solution but end up expensive after you have lost a processor or two by managing to either destroy the chip or activating the code lock feature. May lack a verify phase, resulting in a lot of debugging of perfectly good code, because the contents of the chip doesn't match the linked output.

A kitcen table programmer may use a serial port. Or USB. Or RS232. It may use ISP or use high-voltage programming. It's just that it is a home-built and/or home-designed product of unknown quality. If home-built - how will the user know if it is correctly built, or if any problems is in at the receiver end?