Traditionally, “belting” is the Broadway term for singing in mainly chest voice, as opposed to “legit,” which is the Broadway term for singing in mainly head voice, resembling classical singing.
Today, belting has become synonymous with the sound of musical theater, and when done right, which is a belt-mix, it is very appealing. Even in revivals of musicals from the "legit era" of the 40s, 50s and early 60s, a belt-mix is usually the preferred choice, and instead the style of music gives a perception of "legit." The resembling of classical singing is replaced with a chest quality with head voice mixed in. When going up, the bridges are acknowledged as they should in every style of singing.
In belting, just as in other music genres that resonate beginning in chest, it is vital to use mix towards and in the bridges and above to keep the larynx down and allow for the higher pitches in a healthy and attractive way. If not, belting becomes yelling in and above the first bridge, and very tiring and damaging for the vocal cords.
It might be worthwhile to mention that the way the term "belting" is used in general today, it is a specific sound and genre of music that is referred to, not a specific technique. It differs from other popular music genres, where each singer's unique sound, style, and quality is what makes them the artists they are, and it is of paramount importance to not take their individuality away from them. But just like musical theater differs from other popular music genres by not allowing for individual musical choices or improvisation, belting is a more uniform sound where the singer's personal characteristics are toned down in favor of the overall sound.
Our approach to belting technically has the same principles as our approach to all genres of music, however, the genre is a stylistic choice rather than a technical choice.
You wouldn't for instance refer to pop- and R&B singers like Adele, Rihanna and Alicia Keys as belting, although they sing mainly in chest voice. However, to use the term belting to describe their singing, isn't done since they have characteristic, individual sounds.
Belting is usually nowadays isolated to describe Broadway, or musical theater type singing sung mainly in chest voice, but where the singers' individual characteristics aren't necessarily easy to tell apart. The goal for someone who wants to be regarded "belting," is to sound "Broadway," rather than any one individual way, which would rather be referred to as pop.