In simple terms, Par refers to the number of strokes a golfer is expected to finish the game. This could be in terms of a single hole or all the holes in the entire course which could be 9 or 18 in most cases.
Par is the most used word in golf
What the value should be to represent the bar is usually derived from 2 putts and the number of strokes to reach the green from the starting point. In most cases, you will find holes being labelled as par-3, par-4 or par-5. Par-6 is sometimes used although it is not very common.
Naturally, this means that a par-4 hole would be longer than a par-3 hole and so on. For instance, if a hole is listed as par-3, it simply means that you will be expected to use one stroke to hit the ball to the green. Then, 2 putts will be all you need to put the ball into the hole.
The 2 putts here is standard. If the hole is a par-5, it means you will take 3 strokes to reach the green and 2 putts to put it into the hole.
If you are playing in an 18-hole course, it would range between 69 and 74. The more common ones are par-70, par-71 or par-72.
If you are playing on a par-70 game and completed it within 68 strokes (plus the 2 putts), then you would have been said to have finished it 2-below par. The same will be applied if you needed more strokes to complete the hole. If you took more than 1 stroke to complete a par-5 hole, you will be said to have completed it 1-over par.
If you have completed a par-3 hole with the 3 strokes expected, you will be said to have parred the hole and that has a lot of credibility to it. Sometimes, it is called level par or even-par.