The dictionary defines a shaman as:
A member of certain tribal societies who acts as a medium between the visible world and an invisible spirit world
and who practices magic or sorcery for purposes of healing, divination and control over natural events.
(AMERICAN HERITAGE DICTIONARY)

A priest or priestess who uses magic for the purpose of curing the sick, divining the hidden and controlling events.
(MERRIAM WEBSTER’S DICTIONARY)

Another term commonly used was “witch doctor”, which of course is derogatory and generally comes from the mouths
of non believers and agnostics. Note that agnostic [Greek] means “not knowing” and is not a religious term per se.

So, a shaman is a practitioner of healing who uses methods native to his tribe or culture.
I say this, because most shamans, (but not all) are men.
The term is gender neutral, and describes those people who have one foot in the physical world
and one foot in the world beyond the physical or metaphysical world. Meta,
A prefix of Greek derivation; meaning above or beyond, or one that transcends.

Shamans use a variety of methods and tools to heal, predict and influence events.
All generally use more then one method.
These may includes the use of herbs, plants, sound, songs and chants, prayer,
direct sending of energy, and shaman’s breath.

Shamans are working for the good, and fall under the new age title of lightworkers.
A shaman is a bridge to the other side.
If we look to the past, the council of high priests in ancient Rome were known as the pontifex,
(From Latin pons for bridge).
Indeed, the term for the Pope is “The Pontiff”, or “bridge” to [the other side].

So, it would be correct to say that the only difference between a shaman and a priest is the method
used to arrive at the same end. Priests only use prayer, while shamans have many more tools available to them.
The most powerful shaman are those born with the “gift”.
My personal belief is that “white men” who read books on shamanism are fooling themselves.
I have noted recently an upsurge in fools who have taken a trip on some psychedelic drug
and think that the tiny bit of knowledge obtained makes them a shaman.
My advice is give these people wide berth and do not let them into your energy field.
That being said, I have met non-natives born with the “gift”, both men and women can have the power.
The spirit is world is not male oriented like human societies.

I will point out though, that some Native American elders object to the term shaman, because it is not
a native word or term. The term comes to the English language via Siberia and has roots back to writings in Sanskrit.
I use the term shaman because it has become somewhat generic in our society, and conjures up a vision that is more
inclusive of today’s healers, then the term “medicine” man.
Aside from that, one who calls himself a medicine man is likely to run afoul of the doctor’s lobby,
the AMA and the DEA.