From section 6: "What is the difference between an abstract machine and a virtual machine? In a companion article [1], we propose to distinguish them based on the notion of instruction set: A virtual machine has an instruction set whereas an abstract machine does not. An abstract machine directly operates on a λ-term, but a virtual machine operates on a compiled representation of a λ-term, expressed using an instruction set."
http://www.brics.dk/RS/03/13/BRICS-RS-03-13.pdf
From section 6: "What is the difference between an abstract machine and a virtual machine? In a companion article [1], we propose to distinguish them based on the notion of instruction set: A virtual machine has an instruction set whereas an abstract machine does not. An abstract machine directly operates on a λ-term, but a virtual machine operates on a compiled representation of a λ-term, expressed using an instruction set."
[1] "From Interpreter to Compiler and Virtual Machine: A Functional Derivation": http://www.brics.dk/RS/03/14/BRICS-RS-03-14.pdf