What is meant by semi custom cabinets for a kitchen? ?

Semi-custom are considered a little better than "stock" cabinets; more solid wood instead of veneers on the faces, maybe a better grade of shelving, etc. Fully custom cabinets are generally made by cabinet makers or cabinet shops. Your scenario of a 40" base is right on. It is an odd size, so that would be a custom cabinet. If you're looking to keep costs down, stock cabinets are your lowest price, but they can still be great looking cabinets. Most cabinets come in 3" intervals, so if you need 40" you would buy perhaps 39" and then use a filler for the remaining gap. Regarding the demo, other than your time; it's not a big deal. You might consider having a plumber and electrician disconnect stuff before you start. Also, wall cabinets are heavy, so a helper is a great idea. Go for it!  more