I don't think we have an all-embracing definition. I'd go with something along the lines of a phenomenon of replicating evolving metabolism. Not all life is conscious but all life metabolises, all life replicates, and all life evolves.
Life first started with the replicating DNA/RNA. That is the beginning of the survival instinct that is an essential part of all Life. From this survival instinct, were probably derived the procreation and parental instincts.
The question is, why did Life first begin? We have no means of knowing for sure, of course. Merely saying that replication is an emergent property of DNA is a cop out. It is just an observation...and does not explain anything.
We cannot also be sure if the DNA replication happened only in one place and one time, from where it spread all around the world...or whether similar replication happened in many places around the world.
Be that as it may, it is possible (philosophically) to meaningfully speculate that something reacted or entered or coupled with the DNA/RNA and made it behave in the way it did. From there Life started.
This something is what we call Prana....a kind of Life globule (containing some form of energy) that is believed to exist everywhere and which makes life prevail. It makes Life always find a way!
Of course, lots of questions can be asked about the nature of the Prana, its chemical composition, where did it come from, how and why does it enter organic matter, why not inorganic matter...and so on and so forth. There are no answers.
The point is that this idea not only attempts an answer to the question of how Life came about ...but that it also explains many forms of healing, health generating techniques etc. like Yoga, Pranayama (breathing exercises) and meditations which are are all based on an understanding of how this Prana works and moves around the body. And all these techniques work!
I remember that Neil Tyson the astrophysicist was recently asked whether Life could exist in an amorphous form. He said that it is possible.
It is time scientists started thinking laterally and started investigating such matters.
Just some thoughts.