RTF stands for Ready-to-Fly and it means the model you are buying comes complete with everything you need to get started - straight from the box!
BNF stands for Bind-N-Fly. Bind-N-Fly products come with everything you need except for a transmitter. With BNF products you can use the transmitter of your choice and bind it to the receiver included with the model.
PNP stands for Plug-N-Play. Plug-N-Play products come with everything you need except for a transmitter, receiver battery and charger. It does contain servos, motor and ESC.
ARF stands for Almost-Ready-to-Fly, this means the model needs some additional "need to complete" items before you can start flying. Common additional items include servo's, motor, electronics, batteries and even glue.