Suits have what is called a "drop," which is the difference between the size of the jacket and the size of the pants.
Classic-fit and Modern Fit suits typically have a 6" drop, meaning that a size 38R jacket is paired with size 32 pants.
Slim-fit suits typically have a 7" drop, meaning that a 38R jacket is paired with size 31 waist pants.

London (Hybrid) Fit:
The London (hybrid) fit is typically a little more generous around the chest and armholes, yet also allows a little extra room at the mid-section, while MAINTAINING a slim-look silhouette.

Classic (Sierra) Fit:
The Traditional or Classic fit is typically a little more generous in its form. Meaning that this fit allows a fair amount of room at the mid-section, and also has a slightly longer jacket.

Moderna Fit:
A Modern Fit suit is trimmer through the torso, with a narrower lapel, slightly shorter jacket, and flat front pants that provide a fantastic trimmer look.
The greatest thing about a Modern Fit suit is that you do not have to be thin to look good in it- This fit is a look that can flatter all kinds of physiques.
The body-contouring cut through the chest and midsection makes you look trimmer, no matter what your height or weight.

Slim Fit:
Slim fit suits allow for a slimmer waist in jackets and narrower pant legs at the hips.
These types of suits generally apply to the slim man, however, it also applies to the men intent on the ultra-slim silhouette.