One of the most common questions that I receive for saxophones is "what does ribbed body construction mean?"
On a saxophone, every key is suspended up from the body by no fewer then 2 posts. These posts can be attached to the body of the saxophone in one of two ways.
Post To Body - Each post is individually soldered on to the body.
Ribbed Body - Large groups of posts are soldered to a large plate of brass, aka a "rib". This "rib" is then soldered on to the body.
With ribbed construction, you add more weight to the saxophone. This changes the vibration of the instrument. Typically, ribbed body saxophones will give a warmer overall sound because of the added weight.
Ribbed is not always better!
It is a common misconception that ribbed is better. The reason behind this is that all student level saxes are post to body construction. Most intermediate models are ribbed. So many sales persons will use this as an explanation as to why the intermediate model is more expensive, quoting it as better.
There are many professional model saxophones that do not use ribbed construction. Keep in mind that the weight of the sax can negatively effect the playability if the construction is too heavy for the design.
The design of a sax effects the tone of the sax more then the weight does. So if you have a design that by nature is already dark in tone, then adding more weight can actually be a negative thing.
For instance, all modern professional Keilwerth saxophones do not use ribbed body. Instead they use post to body construction. Many vintage professional horns also did not use ribbed construction.
Post to body models vibrate easier then ribbed body models. This is why student models are made this way, it makes it easier for a basic beginner to play. However, depending on the design of the sax, the more vibrant body may be the better bet.