LCD - Liquid Crystal Display (same as your Casio wrist watch), can't be seen without back-lightling, so they use very thin & long fluorescent tubes. If you look inside the cooling vents, they can be seen. LCD with LED back-lighting substitutes LED's for the fluorescent tubes. Fluorescent tubes wear out, LED's do not.
LED - Light Emitting Diode. They produce their own light. Most displays (monitors & TV's) are transitioning to these.
ISP - Internet Service Provider
Any screen can show more columns, but they all work best at their "native resolution". Anything 20" & larger is usually 1600x900, for full High Definition (HD). If your 23 & 27 both are 1600x900, everything will appear larger on the 27, if both are set at 1600x900. You can set the resolution higher, but the images can get fuzzy.