It's a load that someone, usually a gun writer, has found that works well in his rifle and it is a bit different than found in most reloading books. Often it's a little heavier than found in the regular loading charts.
A similar type book that came out in 1978 was, "Game Loads and Practical Ballistics for the American Hunter," by Bob Hagel. I have seen this book condemned because it is stated the loads he gives are too heavy. I have had this book from near day one and have found it very helpful. It covers many useful subjects on shooting, as well as reloading to get the most from your rifle, whether varmint or big game rifle. Some of his loads may seem pretty steep, if you are used to only the mainline loading manuals, but he always states the rifle he used to arrive at his loads. In 243, 270 and 30-06 I have used his exact loads in the bolt action rifles of those calibres I have/had and found no loading of his to give me signs of excess pressure.