1. An exact duplicate: “Our product is a clone of their product.” Implies a legal reimplementation from documentation or by reverse-engineering. Also connotes lower price.
2. A shoddy, spurious copy: “Their product is a clone of our product.”
3. A blatant ripoff, most likely violating copyright, patent, or trade secret protections: “Your product is a clone of my product.” This use implies legal action is pending.
4. [obs] PC clone: a PC-BUS/ISA/EISA/PCI-compatible 80x86-based microcomputer (this use is sometimes spelled klone or PClone). These invariably have much more bang for the buck than the IBM archetypes they resemble. This term fell out of use in the 1990s; the class of machines it describes are now simply PCs or Intel machines.
5. [obs.] In the construction Unix clone: An OS designed to deliver a Unix-lookalike environment without Unix license fees, or with additional ‘mission-critical’ features such as support for real-time programming. Linux and the free BSDs killed off this product category and the term with it.
6. v. To make an exact copy of something. “Let me clone that” might mean “I want to borrow that paper so I can make a photocopy” or “Let me get a copy of that file before you mung it”.