What do rail-to-rail input and output mean for an op-amp?
An op-amp with a high rail input is able to deal with input signals up to +VCC. While a low rail input is able to deal with signals down to -VCC. Rail-to-rail input op-amps can handle input signals from -VCC to +VCC. Rail-to-rail output is the capability of an op-amp to drive its output very close to the power supply rails.