Is there a standard definition for life?

The Turing Test is one standard to determine if a machine is a sentient being.

*Turing test is a test of a machine's ability to demonstrate intelligence. It proceeds as follows: a human judge engages in a natural language conversation with one human and one machine, each of which tries to appear human. All participants are placed in isolated locations. If the judge cannot reliably tell the machine from the human, the machine is said to have passed the test. In order to test the machine's intelligence rather than its ability to render words into audio, the conversation is limited to a text-only channel such as a computer keyboard and screen.[1] The test was proposed by Alan Turing in his 1950 paper Computing Machinery and Intelligence, which opens with the words: "I propose to consider the question, 'Can machines think?'" Since "thinking" is difficult to define, Turing chooses to "replace the question by another, which is closely related to it and is expressed in relatively unambiguous words."[2] Turing's new question is: "Are there imaginable digital computers which would do well in the [Turing test]"?[3] This question, Turing believed, is one that can actually be answered. In the remainder of the paper, he argued against all the major objections to the proposition that "machines can think".[4] In the years since 1950, the test has proven to be both highly influential and widely criticized, and it is an essential concept in the philosophy of artificial intelligence.[5] To date, there are no machines that can convincingly pass the test.[6] > http://en.wikipedia.org/wiki/Turing_test*

The biological definition of life, from Wikipedia, is:

... life is the condition which distinguishes active organisms from inorganic matter. Living organisms undergo metabolism, maintain homeostasis, possess a capacity to grow, respond to stimuli, reproduce and, through natural selection, adapt to their environment in successive generations. More complex living organisms can communicate through various means.

The last sentence above addresses what Robert's post mentioned -- sentience.

There are also different definitions of life used when discussing philosophy or religion, due to differing views of how life relates to existence and consciousness as well as topics such as the meaning of life, the origin of life (a god or gods), the existence of a soul or afterlife, etc.

And as "life" relates to declaring a person living or dead, there are different criteria used to determine life/death in medicine and law -- see death (the medical condition) and legal death.

Always trying to catch up and when you finally do you catch up you fall behind.