Difficult to describe. I'll post a text underneath that I feel does tell it really well.
First I want to make clear I mean no judgement with 'advanced'.
A Lightworker is anyone who devotes their life to being a bright light in the world. They understand that their actions (no matter how big or small) have the potential to raise the vibration of the planet. A Lightworker soul is awake, conscious that their presence matters and that they are part of something that is bigger than them.
Lightworkers are not just tie-dye wearing hippies and healers with dreads. Far from it. They are teachers and chefs, writers and singers, producers and cleaners, mothers and mediums. They’re at the country club and the nightclub, in the cafe and crèche, the boardroom and the art room.
A Lightworker is someone who makes a conscious decision to endeavour to answer the call of Source (light) over the call of the ego (fear).
There are two types of energy on this planet. Light and dark. Light energy is unlimited and comes from Source. It’s high vibrational, expansive and full of love. Dark energy is much more dense. It’s the manipulation, power struggle and fear. It sees us all as separate, rather than connected spiritual beings. It goes against the flow of The Universe.
Lightworkers turn their light on by following what lights them up and then effortlessly sharing that light with the world around them. They are in tune with the callings of their soul and act on its whispers regardless of fear. They do not need to convince anyone of anything, rather just be the light.
This is from Rebecca Campbell, who made the Work Your Light oracle card deck.
There's more on her site, where she describes two types of Lightworker (not that dark one, I personally don't see that as a Lightworker).
https://rebeccacampbell.me/what-is-a-lightworker/