There is not a publicly published complete and explicit definition of the letters Cisco uses in their product nomenclature. the best one can do is look at either the product data sheet or Cisco Commerce Workspace (partner / reseller only) and see what the product description is.
For instance, WS-C3650FS (-E or -L) is "Cisco Catalyst 3650 48 Port Full PoE 4x1G Uplink IP Services" (with Enhanced or Lanbase license), WS-C3650-48TQ is "Cisco Catalyst 3650 48 Port Data 4x10G Uplink IP Services" and WS-C2960X-48FPD-L is "Catalyst 2960-X 48 GigE PoE 740W, 2 x 10G SFP+, LAN Base".
WS generally is a prefix on part numbers for all Wire Speed switch products. (Though that breaks down a bit on some of the smaller Catalyst models.) I've also seen it refer to "Workgroup Switch" class products.
FS means is is a switch with fiber user ports.
X distinguishes the newer 2960 models from the original 2960 series.
FPD-L mean it has Full PoE+ and comes with Lanbase software feature license.
Generally the letters at the end refer to the uplink type and license level.
Also please see this earlier discussion:
https://supportforums.cisco.com/thread/2135341
