One that tilts up and down but doesn’t flip out and rotate in all directions (an ‘articulating’ screen). Tilting screens are nonetheless useful for composing pictures with the camera at waist or ground level or above head height.
OLED stands for ‘organic light emitting diode’. It’s a more advanced display tech than regular LCDs with wider viewing angles, faster response, better brightness and reduced power consumption. The OLED electronic viewfinder is a selling point in the Fujifilm X-T1, for example.
Where the camera displays what the sensor is capturing either on the rear LCD or in an electronic viewfinder. All compact cameras and mirrorless cameras are effectively in ‘live view’ all the time. It’s only out of the ordinary on a DSLR, which has to go into a special mirror-up ‘live view’ mode.
Some DSLRs have an LCD status panel on the top plate for basic shooting information, battery life remaining and other items. This uses a high-contrast display with no backlighting to save power, but it can be hard to see in dim light, so there’s usually a backlight switch too.
The key specs here are the size, measured across the diagonal, and the resolution, measured in thousands of dots. For example, you might get a 3-inch LCD with 921k (921,000) dots.