The Raspberry Pi 2 Model B is the second generation Raspberry Pi.
It replaced the original Raspberry Pi 1 Model B+ in February 2015.
Compared to the Raspberry Pi 1 it has:

A 900MHz quad-core ARM Cortex-A7 CPU
1GB RAM

Like the (Pi 1) Model B+, it also has:

4 USB ports
40 GPIO pins
Full HDMI port
Ethernet port
Combined 3.5mm audio jack and composite video
Camera interface (CSI)
Display interface (DSI)
Micro SD card slot
VideoCore IV 3D graphics core

The Raspberry Pi 2 has an identical form factor to the previous (Pi 1) Model B+ and has complete compatibility with Raspberry Pi 1.

Source: raspberrypi.org