CRT (cathode ray tube) is a proven, cheaper, older technology that uses a tv tube. good crt monitors can be had for under $200 (USD).
TFT (thin film transistor) is a newer, more expensive technology for flat panel LCD-type displays. tft displays have a reaction time spec, for gaming you'll want a reaction time of no more than 12ms. a good tft display will usually run you upwards of $400 (USD)
it generally costs nearly half as much to get a tft display's crt equivalent.