Q: What is the difference between IP address and machine address, in brief?
A: According to an IPv4 version of the Internet Protocol (IP), as opposed to an IPv6 version, an IP address is defined below:
"An IP address is a 32-bit number that identifies each sender or receiver of information that is sent in packets across the Internet.… An IP address has two parts: the identifier of a particular network on the Internet and an identifier of the particular device (which can be a server or a workstation) within that network. On the Internet itself -- that is, between the router that moves packets from one point to another along the route -- only the network part of the address is looked at." -- Steve Spence, Contributor
A "machine address" is sometimes known as the "host number" or "host address." In the two parts of the IP address described above; the identifier of the network is the "network number" while the identifier of the device is the "machine address" or "host number." To view an example of this, I recommend reading the WhatIs.com definition of 32-bit IP addressing.
Now, we can conclude the difference between an IP address and a machine address: In brief, the machine address is only one part of the IP address that identifies a location of a machine, and the IP address consists of numbers which identify a network as well as a computer machine.
If you'd like to learn more about IP addressing, I recommend this short tutorial on IP addressing and subnetting.