A Japanese saw is a thin-bladed hand saw that cuts on the pull stroke, unlike most other hand saws used in the U.S. and Europe that cut on the push stroke. Because they cut on the pull stroke and thus are not subject to compression tension, Japanese saws have thinner, more flexible blades than their Western counterparts. This results in a thinner kerf, less effort to remove material, and often finer control over the cut. Push saws require a thicker blade to remain rigid; otherwise, they would flex during the cut and bind.
There are several different types of Japanese saws. Two of the most common are the Dozuki and the Ryoba. Other types include the Azebiki and Mawashibiki. The Dozuki saw has the thinnest blades of all Japanese saws. One side of the blade contains the teeth and the other end has a reinforcing backer strip of steel that enhances rigidity during the cut. It is a good choice for cutting dovetails, tenons and other fine joinery.
The Ryoba saw is two-sided: one side for ripping and the other for cross-cutting. It works well for surface cuts (such as sawing off wooden plugs for screw holes) as well as for general purpose cutting.
Amateur woodworkers often find a Japanese saw easier to use than a push saw. This is probably because you are controlling the saw with your fingertips rather than the heel of your hand. It is often easier to pull than to push — how many times have you skinned your knuckles when pushing rather than pulling a wrench to loosen a nut? Also, the extremely sharp teeth and thin kerf make for low effort cutting. On the other hand, if you have a bunch of 2×10’s to cross cut, a western style push saw will often outperform a Japanese saw, assuming its well tuned and sharpened. It’s all about getting the right tool for the job.
Japanese saws range considerably in price but you can get a decent working-man’s saw for under $20. It will likely give you years of service and be a fine compliment to the other saws in your toolbox.