Philosophers have been interested in consciousness for a much longer time than scientists. So, from a philosophical perspective, there are several different answers to the question - what does consciousness mean?
Philosophers try to answer questions about the nature of consciousness - what kind of entity is it? Is it real and if so, what is the nature of its reality? Is it fundamental to life or is it a by-product of certain kinds of biological organisation such as found in human brains? Can a machine ever be conscious?
In humans, at least, consciousness expresses itself through a mind and a mind requires a body. Mind and body go together. Then it gets tricky, because mental objects, events and processes that we can perceive such as thoughts, feelings, images and memories are all a completely different kind of thing when compared to physical objects, events and processes that we can see, hear, touch, smell or taste. In the conscious life of humans and likely the higher animals, one kind of reality - the physical world - is connected to another kind of reality - the mental world. But how does this happen?
The actual experience of “red”, for example, is a completely different kind of thing to the particular wavelength of visible light that it is associated with, or to the physical and chemical changes that take place at the back of the eye when the red light is received, or to the changes in the firing of neurons in certain parts of my brain which might “correlate” with my experience of the colour red.
This philosophical puzzle is called the mind-body problem. In relation to the scientific understanding of consciousness it has been called “the hard problem” of consciousness. Science can map the correlation between mental experience and brain function alright but how can we explain those connections? If we can't answer that then we can't answer the question - what does consciousness mean?
Different philosophical systems approach this problem in different ways:
The materialist or physicalist approach which underpins modern science takes the physical world to be the primary reality. Consciousness is therefore seen as an emergent property of highly organised and complex biological systems.
The idealist approach treats mind as the primary reality - either the mind is held to be a kind of subtle substance or else everything is thought of as being made of knowledge forms of one kind or another.
The panpsychist approach says mind and body are equally real and every physical entity has an outer nature (the physical part) and an inner nature (an associated mental state).
Whichever approach is taken, the philosophical answer to the question "what does consciousness mean?" involves solving the mind-body problem.