Non-modular
The PSU comes with ALL possible cables attached to it, ready to go.
This has the advantage of ensuring you're not going to need a cable.
The downside is that it's VERY messy for cable-management. Trying to find a place for all the excess cables can be a nightmare. Bad cable-management can mean the difference between good or bad airflow and consequently the operating temperature of your system.
Semi-modular
Only the essential cables come pre-attached. Usually this means, 24Pin ATX, a single PCIe, 8Pin CPU, and maybe one or two peripheral power cables (SATA/Molex). There's less clutter and it is definitely much better than non-modular and a cheaper solution than going full modular.
Full Modular
Comes with no cables pre-attached. You only attach the ones you need.
It is more expensive, but also gives you more options, allowing you to only install the cables you need and keep airflow and cable management to a maximum. All newer generation HALE PSUs are fully modular.